Surgical method and apparatus for positioning a diagnostic or therapeutic element within the body and pressure application probe for use with same

ABSTRACT

A surgical method and apparatus for positioning a diagnostic or therapeutic element within the body. The apparatus may be catheter-based or a probe including a relatively short shaft.

BACKGROUND OF THE INVENTIONS

1. Field of Invention

The present inventions relate generally to structures for positioningone or more diagnostic or therapeutic elements within the body and, moreparticularly, to devices which are particularly well suited fortreatment of cardiac conditions.

2. Description of the Related Art

There are many instances where diagnostic and therapeutic elements mustbe inserted into the body. One instance involves the treatment ofcardiac conditions such as atrial fibrillation and atrial flutter whichlead to an unpleasant, irregular heart beat, called arrhythmia.

Normal sinus rhythm of the heart begins with the sinoatrial node (or “SAnode”) generating an electrical impulse. The impulse usually propagatesuniformly across the right and left atria and the atrial septum to theatrioventricular node (or “AV node”). This propagation causes the atriato contract in an organized way to transport blood from the atria to theventricles, and to provide timed stimulation of the ventricles. The AVnode regulates the propagation delay to the atrioventricular bundle (or“HIS” bundle). This coordination of the electrical activity of the heartcauses atrial systole during ventricular diastole. This, in turn,improves the mechanical function of the heart. Atrial fibrillationoccurs when anatomical obstacles in the heart disrupt the normallyuniform propagation of electrical impulses in the atria. Theseanatomical obstacles (called “conduction blocks”) can cause theelectrical impulse to degenerate into several circular wavelets thatcirculate about the obstacles. These wavelets, called “reentrycircuits,” disrupt the normally uniform activation of the left and rightatria.

Because of a loss of atrioventricular synchrony, the people who sufferfrom atrial fibrillation and flutter also suffer the consequences ofimpaired hemodynamics and loss of cardiac efficiency. They are also atgreater risk of stroke and other thromboembolic complications because ofloss of effective contraction and atrial stasis.

Although pharmacological treatment is available for atrial fibrillationand flutter, the treatment is far from perfect. For example, certainantiarrhythmic drugs, like quinidine and procainamide, can reduce boththe incidence and the duration of atrial fibrillation episodes. Yet,these drugs often fail to maintain sinus rhythm in the patient.Cardioactive drugs, like digitalis, Beta blockers, and calcium channelblockers, can also be given to control the ventricular response.However, many people are intolerant to such drugs. Anticoagulant therapyalso combats thromboembolic complications, but does not eliminate them.Unfortunately, pharmacological remedies often do not remedy thesubjective symptoms associated with an irregular heartbeat. They also donot restore cardiac hemodynamics to normal and remove the risk ofthromboembolism.

Many believe that the only way to really treat all three detrimentalresults of atrial fibrillation and flutter is to actively interrupt allof the potential pathways for atrial reentry circuits.

One surgical method of treating atrial fibrillation by interruptingpathways for reentry circuits is the so-called “maze procedure” whichrelies on a prescribed pattern of incisions to anatomically create aconvoluted path, or maze, for electrical propagation within the left andright atria. The incisions direct the electrical impulse from the SAnode along a specified route through all regions of both atria, causinguniform contraction required for normal atrial transport function. Theincisions finally direct the impulse to the AV node to activate theventricles, restoring normal atrioventricular synchrony. The incisionsare also carefully placed to interrupt the conduction routes of the mostcommon reentry circuits. The maze procedure has been found veryeffective in curing atrial fibrillation. However, the maze procedure istechnically difficult to do. It also requires open heart surgery and isvery expensive. Thus, despite its considerable clinical success, only afew maze procedures are done each year.

More recently, maze-like procedures have been developed utilizingcatheters which can form lesions on the endocardium to effectivelycreate a maze for electrical conduction in a predetermined path.Exemplary catheters are disclosed in commonly assigned U.S. Pat. No.5,582,609. Typically, the lesions are formed by ablating tissue with anelectrode carried by the catheter. Electromagnetic radio frequency(“RF”) energy applied by the electrode heats, and eventually kills (i.e.“ablates”), the tissue to form a lesion. During the ablation of softtissue (i.e. tissue other than blood, bone and connective tissue),tissue coagulation occurs and it is the coagulation that kills thetissue. Thus, references to the ablation of soft tissue are necessarilyreferences to soft tissue coagulation. “Tissue coagulation” is theprocess of cross-linking proteins in tissue to cause the tissue to jell.In soft tissue, it is the fluid within the tissue cell membranes thatjells to kill the cells, thereby killing the tissue.

Catheters used to create lesions (the lesions being 3 to 15 cm inlength) typically include a relatively long and relatively flexible bodyportion that has an ablation electrode on its distal end. The portion ofthe catheter body portion that is inserted into the patient is typicallyfrom 23 to 55 inches in length and there may be another 8 to 15 inches,including a handle, outside the patient. The proximal end of thecatheter body is connected to the handle which includes steeringcontrols. The length and flexibility of the catheter body allow thecatheter to be inserted into a main vein or artery (typically thefemoral artery), directed into the interior of the heart, and thenmanipulated such that the ablation electrode contacts the tissue that isto be ablated. Fluoroscopic imaging is used to provide the physicianwith a visual indication of the location of the catheter.

Atrial appendages are primary potential sources of thrombus formation.The atrial appendages are especially important in the transport of bloodbecause they have a sack-like geometry with a neck potentially morenarrow than the pouch. In this case, contraction of the appendage isessential to maintain an average absolute blood velocity high enough toeliminate potential stasis regions which may lead to thrombus formation.

In the maze procedure performed through open heart surgery, the typicalaccess points into the interior of the atria are the atrial appendages.Therefore, at the conclusion of the surgical procedure, the regionoccupied by the atrial appendages is eliminated by surgically removingthe appendages. This mitigates subsequent problems resulting from bloodstasis in the atrial appendages as well as from electrical isolation ofthe appendages from the rest of the atria. However, as noted above, openheart surgery is very expensive and the incision based maze procedure isdifficult to perform. Although catheter-based procedures do not admitthemselves to surgical removal of the appendages, catheter-basedprocedures and apparatus have been recently developed which repositionthe atrial appendages, affix them in an altered position and/or fuse thewalls of the appendages to one another to isolate the appendages, reducestasis regions and ultimately thrombus formation. Such procedures andapparatus are disclosed in commonly assigned U.S. application Ser. No.08/880,711, filed Jun. 23, 1997, which is a File Wrapper Continuation ofU.S. application Ser. No. 08/480,200, filed Jun. 7, 1995, entitled“Atrial Appendage Stasis Reduction Procedures and Devices” andincorporated herein by reference. One of these procedures involves theuse of a catheter having a lasso which is tightened around theappendage. RF energy is then transmitted to the appendage by way of thelasso to thermally fuse the walls of the appendage to one another,thereby isolating the appendage.

It is believed the treatment of atrial fibrillation and flutter requiresthe formation of long, thin lesions of different lengths and curvilinearshapes in heart tissue. Such long, curvilinear lesion patterns requirethe deployment within the heart of flexible ablating elements havingmultiple ablating regions. The formation of these lesions by ablationcan provide the same therapeutic benefits that the complex incisionpatterns that the surgical maze procedure presently provides, butwithout invasive, open heart surgery.

With larger and/or longer multiple electrode elements comes the demandfor more precise control of the ablating process. The delivery ofablating energy must be governed to avoid incidences of tissue damageand coagulum formation. The delivery of ablating energy must also becarefully controlled to assure the formation of uniform and continuouslesions, without hot spots and gaps forming in the ablated tissue.

The task is made more difficult because heart chambers vary in size fromindividual to individual. They also vary according to the condition ofthe patient. One common effect of heart disease is the enlargement ofthe heart chambers. For example, in a heart experiencing atrialfibrillation, the size of the atrium can be up to three times that of anormal atrium.

Catheter-based ablation and atrial appendage isolation have proven to bea significant advance over the conventional open heart surgery basedapproaches. Nevertheless, the inventors herein have determined thatfurther improvements are possible.

For example, and with respect to ablation procedures in particular, theinventors herein have determined that it can be quite difficult toaccurately position an ablation electrode on the endocardium surface bymanipulating the distal end of a relatively long catheter body from aremote handle. This is especially true with respect to left atrialsites. The present inventors have also determined that fluoroscopy is asomewhat inaccurate method of visualizing the ablation electrodes duringpositioning and when determining whether the electrodes are in propercontact with tissue.

Additionally, a primary goal of any ablation procedure is to createcontiguous lesions (often long, curvilinear lesions) withoutover-heating tissue and causing coagulum and charring. Tissue ablationoccurs at 50° C., while over-heating occurs at 100° C. The presentinventors have further determined that it can be difficult to producetissue contact that will accomplish this result with an electrodemounted on the distal end of a relatively long catheter. This isespecially true in those procedures where an electrode on the distal tipof the catheter is dragged along the tissue. Such dragging also makesaccurate placement of the electrode very difficult. Other shortcomingsidentified by the present inventors concern the convective coolingeffects of the blood pool on the electrodes. For example, the systempower requirements must be high enough to compensate for the heat lossesdue to convective cooling.

One proposed method of solving the over-heating problems associated withconventional ablation catheters is the so-called “cooled tip” approach.Here, the tissue surface is cooled with a saline solution. Although thesaline is somewhat useful in keeping the surface temperature below theover-heating temperature, the sub-surface tissue temperature can stillrise well above 100° C. Such temperatures will cause gas within thesub-surface tissue to expand. Ultimately, the tissue will tear or pop,which will result in perforations of the epicardial surface and/or thedislodging of chunks of tissue that can cause strokes.

Turning to atrial appendage isolation, the present inventors havedetermined that catheter-based procedures suffer from many of the samedisadvantages discussed above, such as those concerning positioning andvisualization. Additionally, the inventors herein have determined thatthe lasso can bunch up the tissue when the lasso is tightened and thattissue fusion would be improved if this bunching could be avoided.

With respect to energy control, conventional ablation devices includecontrols that are located either on the RF energy source, or on a footpedal. The inventors herein have determined that such arrangements areinconvenient and can make it difficult to control power during asurgical procedure.

Turning to surgical procedures in general, one problem associated withmany surgical procedures is excessive bleeding. For example, a highlevel of bleeding is often associated with the removal of liver lobesand certain cancerous tumors. The inventors herein have determined thatpresent surgical methods could be improved in the area of blood loss.

SUMMARY OF THE INVENTIONS

Accordingly, the general object of the present inventions is to providean apparatus for positioning an operative element (such as an ablationelectrode) within the body which avoids, for practical purposes, theaforementioned problems. In particular, one object of the inventions isto provide tissue ablation systems and methods providing beneficialtherapeutic results without requiring highly invasive surgicalprocedures. Another objective of the inventions is to provide systemsand methods that simplify the creation of complex lesions patterns insoft tissue, such as myocardial tissue in the heart.

In order to accomplish these and other objectives, certain embodimentsof one of the present inventions include an electrode support structurecarried at the distal end of a guide body. The support structureincludes a bendable stylet extending along an axis outside the distalend of the guide body. The structure also includes at least one flexiblespline leg having a near end attached to the distal end of the guidebody and a far end extending beyond the distal end of the guide body andattached to the bendable stylet. The spline leg is normally flexedbetween the distal guide body end and the bendable stylet in a firstdirection that extends along and radially outward of the axis of thestylet. At least one electrode element is on the flexible spline. Thestructure further includes a control element to apply tension to thestylet. The tension bends the stylet, thereby flexing the spline leg ina second direction.

The flexure of the spline leg in the first direction facilitatesintimate contact between the electrode element and tissue. Theadditional flexure by the stylet of the spline leg in the seconddirection makes possible the creation of a diverse number of additionalshapes and tissue contact forces.

In accordance with another embodiment of one of this invention, anelectrode support structure is provided that, in addition to bending thestylet, includes another control element that moves the stylet along itsaxis to increase or decrease flexure of the spline leg in the firstdirection. This additional control over the flexure of the spline legfurther enhances intimate contact against tissue, regardless ofvariations in the dimensions of the surrounding tissue region.

In accordance with another embodiment of this invention, an electrodesupport structure is provided that includes a malleable stylet. Thephysician imparts a desired flexure to the spline leg in the seconddirection by bending the malleable stylet. Alternatively, an electrodesupport structure is provided in which the spline leg itself ismalleable.

Structures that embody the features of this invention make possible thecreation of diverse number of shapes and contact forces to reliablyachieve the type and degree of contact desired between electrodeelements and targeted tissue areas, despite physiologic differencesamong patients.

Another aspect of this invention is associated with structures andmethods for ablating tissue in a heart. The structures and methodsinclude a probe for deployment within the heart. The probe carries atleast one elongated flexible ablation element to which a bendable styletis attached. The structures and method apply tension to bend the stylet.The bending of the stylet flexes the ablation element into a curvilinearshape along the contacted tissue region. By transmitting ablation energyto the ablation electrode while flexed in the curvilinear shape and incontact with the tissue region, the structures and methods make possiblethe formation of curvilinear lesion patterns in heart tissue.

In order to accomplish the above-described and other objectives, asurgical device in accordance with one embodiment of another one of thepresent inventions includes a relatively short shaft, a bendable splineassembly associated with the distal end of the shaft and having apredetermined configuration, the spline assembly being adapted tocollapse in response to external forces and expand when the forces areremoved, and an operative element associated with the bendable spline.Optionally, a substantially tubular member may be positioned around theshaft. Movement of the substantially tubular member over the splineassembly will cause the spline assembly to collapse, while the splineassembly will expand to the predetermined configuration in response to aretraction of the substantially tubular member.

In order to accomplish above-described and other objectives, an softtissue coagulation probe in accordance with one embodiment of one of theinventions includes a relatively short shaft defining a distal end and aproximal end, a handle associated with the proximal end of the shaft,and at least one soft tissue coagulation electrode associated with theshaft and located in spaced relation to the handle.

In order to accomplish above-described and other objectives, a surgicaldevice in accordance with another embodiment of this invention includesa relatively stiff shaft, a handle associated with the proximal end ofthe shaft, and a distal tip assembly associated with the distal end ofthe shaft, the distal tip assembly including a distal member, which isflexible and/or malleable, and an operative element carried by thedistal member.

In order to accomplish this and other objectives, a surgical device inaccordance with another embodiment of this invention includes a shaft, arelatively stiff tubular member positioned around a predeterminedportion of the shaft and movable relative thereto, a distal tip assemblyassociated with the distal end of the shaft and including a flexibledistal member and an operative element carried by the distal member, anda pivot assembly associated with the distal end of the tubular memberand a distal portion of the tip assembly.

There are many advantages associated with these inventions. For example,the above-described embodiments of this invention may be used in amethod of treating atrial fibrillation wherein access to the heart isobtained by way of a thoracostomy. Here, the operative element is anablation electrode. Such a method may also be used to treat atrialfibrillation during mitral valve surgery wherein access to the heart isobtained through a thoracostomy, thoracotomy or median sternotomy.

The relatively short shaft and manner of insertion allows the ablationelectrode to be easily inserted into the atrium and visually guided tothe desired location. Thus, the ablation electrodes in the presentdevice do not have to be guided by manipulating the relatively longshaft of an endovascular catheter. This makes the positioning of theelectrodes within the heart easier and more accurate. Endocardialvisualization is also improved because surgical methods employing thepresent device allow the endocardium to be viewed directly with thenaked eye, a fiberoptic camera or other imaging modalities. Thiseliminates the need for fluoroscopic images and reduces the amount ofradiation required, as compared to catheter-based procedures. Moreover,the shaft in the present device can be relatively stiff, as compared toa catheter shaft, because the present shaft does not have to travelthrough the tortuous vascular path to the heart. Along with therelatively short length of the present shaft, the additional stiffnessenhances torque transmission and provides superior and more reliableelectrode-endocardium contact force.

Surgical devices in accordance with this invention may also be usedduring procedures, such as valve replacement where the patient is oncardiopulmonary bypass, to create tissue lesions. During bypass, theelectrodes elements will not be in contact with the blood pool and,accordingly, will not be affected by the convective cooling.

Patients can only be on bypass for a period of approximately four hours.Long bypass times are associated with increased morbidity and mortality.Thus, all procedures performed during bypass must be rapidly completed.Surgical devices in accordance with the present invention may include aseries of temperature controlled electrodes that allow a long lesion tobe created in rapid fashion, i.e. in approximately 30 to 120 seconds.The ability of the present surgical devices and techniques to createlesions rapidly allows procedures to be performed during bypass that,heretofore, could not due to the time constraints. For example, aconventional surgical maze procedure takes approximately 12 hours tocomplete (note that a portion of the procedure is performed while thepatient is not on bypass), while such a procedure may be completed inapproximately 5 to 15 minutes with the present devices and methods.

In accordance with another advantageous aspect of this invention, theshaft and/or sheath (if present) may be formed from a malleable materialthat a physician can bend into a desired configuration and remain inthat configuration when released. Although malleable, the stiffness ofsuch material must be at least such that the shaft and/or sheath (ifpresent) will not bend under the forces applied thereto during asurgical procedure. Alternatively, or in addition, the distal end of thedevice may also be malleable, thereby allowing the physician to bend thedistal end of the device into a shape corresponding to the bodilystructure to be acted upon. This is particularly important inendocardial applications because the endocardial surface is typicallynon-uniform with ridges and trabeculae residing in the right and leftatria. There are also dramatic differences between endocardial surfacemorphology from patient to patient and from lesion location to lesionlocation. To create contiguous lesions with a surgical approach, thedevice must either distend the atria to flatten out thenon-uniformities, or the probe must be configured to conform to theatrial surface. There are, however, some regions where the atria cannotbe distended to a flat state because of trabeculae, orifices, andridges. A surgeon can observe the atrial surface and bend the presentmalleable device so as to conform thereto. The distal end may, instead,be spring-like or even rigid if the application so requires.

In order to accomplish the above-identified and other objectives, asurgical device in accordance with one embodiment of another one of thepresent inventions includes a handle having at least one movable handlemember, first and second support members operably connected to thehandle, at least one of the support members being movable with respectto the other support member in response to movement of the at least onemovable handle member, and at least one ablation electrode associatedwith the first support member.

There are many advantages associated with this invention. By way ofexample, this invention is especially useful in a method of isolating anatrial appendage. Access to the atrium may be obtained by, for example,a thoracostomy and the appendage may be captured between the supportmembers. RF energy is then applied to the captured portion of theappendage to thermally fuse the walls of the appendage to one another.This method provides better heating and fusing than the lassocatheter-based approach because the tissue is not bunched up whencaptured between the support members, as it is when the lasso istightened. Additionally, the disadvantages associated with the use ofcatheters in general are also avoided.

A surgical clamp in accordance with one embodiment of another of thepresent inventions includes first and second clamp members, and at leastone electrode associated with at least one of the clamp members. Theclamp may be used to isolate an atrial appendage in a manner similar tothat described in the preceding paragraph with the same advantageousresults. Thereafter, the clamp may be either removed or left in place.

A surgical device in accordance one embodiment of another of the presentinventions includes an energy source, at least one energy transmissiondevice, and a handle including an energy control device coupled to theenergy source and to the at least one energy transmission device. Theenergy control device is adapted to selectively control the transmissionof energy from the energy source to the at least one energy transmissiondevice. Because the energy control device is located on the handle,which is necessarily grasped by the physician during surgicalprocedures, the present surgical device provides more convenient energycontrol than that found in conventional devices.

Alternatively, and in accordance with one embodiment of another of thepresent inventions, energy control may be accomplished through the useof a remote energy control device that is connected to power unit, butlocated in close proximity to the patient or otherwise within thesterile zone of an operating room. Such an arrangement also providesmore convenient energy control than that found in conventional devices.

Additionally, whether the power control interface is located on thehandle of a surgical probe or on a remote control device, the powercontrol aspect of the overall electrophysiological system can be moreconveniently brought into the sterile zone because both the presentsurgical probe and remote control device are both readily sterilizable.Conventional power control interfaces, on the other hand, are part of apower control unit that is not readily sterilizable.

To further improve tissue contact, a pressure application probe inaccordance with one embodiment of another of the present inventions maybe used in conjunction with a probe having an energy transmission deviceon a support member. The pressure application probe includes an elongatemain body portion and an engagement device adapted to releasably engagethe support member. The pressure application probe can be used by thephysician to insure that sufficient tissue contact is realized prior toenergy transmission.

A coupling device in accordance with another of the present inventionscan also be used in conjunction with a probe having an energytransmission device on a support member. One embodiment of the couplingdevice includes a base member adapted to be removably secured to a firstportion of the probe's flexible support member and an engagement deviceconnected to the base member and adapted to be removably secured to asecond portion of the flexible support member. The coupling deviceenables a physician to form a distal loop in the support member whendesired, thereby increasing the flexibility of the probe.

In order to reduce the blood loss associated certain surgicalprocedures, a surgical method in accordance with another of the presentinventions includes the steps of coagulating soft tissue and thenforming an incision is the coagulated tissue. If the incision is nodeeper than the coagulation, the incision will not result in significantbleeding. This process can be repeated until an incision of the desireddepth is achieved.

The above described and many other features and attendant advantages ofthe present invention will become apparent as the invention becomesbetter understood by reference to the following detailed descriptionwhen considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Detailed description of preferred embodiments of the invention will bemade with reference to the accompanying drawings.

FIG. 1 is a plan view of an ablation probe having a full-loop structurefor supporting multiple ablation elements.

FIG. 2 is an elevation view of a spline used to form the loop structureshown in FIG. 1.

FIG. 3 is an elevation view of the distal hub used to form the loopstructure shown in FIG. 1.

FIG. 4 is a side section view of the hub shown in FIG. 3.

FIG. 5 is a perspective, partially exploded view of the spline, distalhub, and base assembly used to form the loop structure shown in FIG. 1.

FIG. 6a is an enlarged perspective view of the base assembly shown inFIG. 5.

FIG. 6b is a side section view of an alternative base assembly for theloop structure shown in FIG. 1.

FIG. 7 is an elevation view of a half-loop structure for supportingmultiple electrodes.

FIG. 8 is an elevation view of a composite loop structure for supportingmultiple electrodes comprising two circumferentially spaced half-loopstructures.

FIG. 9 is an elevation view of a composite loop structure comprising twofull-loop structures positioned ninety degrees apart.

FIG. 10 is an elevation view, with parts broken away, of multipleelectrode elements comprising segmented rings carried by a loop supportstructure.

FIG. 11a is an enlarged view, with parts broken away, of multipleelectrode elements comprising wrapped coils carried by a loop supportstructure.

FIG. 11b is an elevation view, with parts broken away, of multipleelectrode elements comprising wrapped coils carried by a loop supportstructure.

FIG. 12 is a top view of a steering mechanism used to deflect the distalend of the probe shown in FIG. 1.

FIG. 13 is a plan view of a full-loop structure for supporting multipleelectrode elements having an associated center stylet attached to aremote control knob for movement to extend and distend the full-loopstructure.

FIG. 14 is a side section view of the remote control knob for the centerstylet shown in FIG. 13.

FIG. 15 is a plan view of the full-loop structure shown in FIG. 13, withthe control knob moved to extend the full-loop structure.

FIG. 16 is a plan view of a full-loop structure shown in FIG. 13, withthe control handle moves to distend the full-loop structure.

FIG. 17 is a plan view of a half-loop structure for supporting multipleelectrode elements having an associated center stylet attached to aremote control knob for movement to extend and distend the half-loopstructure.

FIG. 18 is a plan view of the half-loop structure shown in FIG. 17, withthe control knob moved to extend the half-loop structure.

FIG. 19 is a plan view of a half-loop structure shown in FIG. 17, withthe control handle moves to distend the half-loop structure.

FIG. 20 is a plan view of a full-loop structure for supporting multipleelectrode elements having an associated center stylet attached to aremote control knob for movement to extend and distend the full-loopstructure, and also having a remotely controlled steering mechanism toflex the center stylet to bend the full-loop structure into acurvilinear shape.

FIG. 21 is a side elevation view of the full-loop structure shown inFIG. 20.

FIG. 22 is an enlarged sectional view, generally taken along line 22—22in FIG. 20, showing the steering wires attached to the center stylet toflex it.

FIGS. 23a and 23 b are side elevation views showing the operation of thesteering mechanism in bending the full-loop structure, respectively, tothe left and to the right.

FIG. 24 is a largely diagrammatic, perspective view of the full-loopstructure bent to the right, as also shown in side elevation in FIG.23b.

FIG. 25 is a plan view of the full-loop structure shown in FIG. 20 andthe associated remote control knob for extending and distending as wellas bending the full-loop structure.

FIG. 26 is a side section view, taken generally along lines 26—26 inFIG. 25, of the control knob for extending and distending as well asbending the full-loop structure.

FIG. 27 is a largely diagrammatic, perspective view of the full-loopstructure when distended and bent to the right.

FIG. 28 is a largely diagrammatic, perspective view of a half-loopstructure with steerable center stylet bent to the right.

FIG. 29 is a plan, partially diagrammatic, view of a full-loop structurefor supporting multiple electrode elements having a movable spline legattached to a remote control knob for movement to extend and distend thefull-loop structure.

FIG. 30a is a section view, taken generally along line 30 a—30 a in FIG.29, of the interior of the catheter body lumen, through which themovable spline leg passes.

FIG. 30b is a side section view of an alternative way of securing thefull-loop structure shown in FIG. 29 to the distal end of the cathetertube.

FIG. 31 is a plan, partially diagrammatic view of the full-loopstructure shown in FIG. 29 being extended by pulling the movable splineleg inward.

FIGS. 32 and 33 are plan, partially diagrammatic views of the full-loopstructure shown in FIG. 29 being distended by pushing the movable splineleg outward.

FIGS. 34 and 35 are largely diagrammatic views of the full-loopstructure shown in FIG. 29 being distended by pushing the movable splineleg outward while deployed in the atrium of a heart.

FIGS. 36, 37, and 38 are plan, partially diagrammatic views of afull-loop structure for supporting multiple electrode elements havingtwo movable spline legs attached to remote control knobs for coordinatedmovement to extend and distend the full-loop structure.

FIG. 39a is a plan view of a full-loop structure for support multipleelectrode elements having a smaller, secondary loop structure formed inone spline leg.

FIG. 39b is a side view of the full-loop structure shown in FIG. 39a,showing the smaller, secondary loop structure.

FIG. 40a is a perspective view of a modified full-loop structure forsupporting multiple electrode elements having an odd number of three ormore spline legs.

FIG. 40b is a top section view of the base of the full-loop structureshown in FIG. 40a.

FIGS. 41, 42, and 43 are plan, partially diagrammatic, views of abifurcated full-loop structure for supporting multiple electrodeelements having movable half-loop structures to extend and distend thebifurcated full-loop structure.

FIGS. 44 and 45 are plan, partially diagrammatic, views of analternative form of a bifurcated full-loop structure for supportingmultiple electrode elements having movable center ring to extend anddistend the bifurcated full-loop structure.

FIG. 46 is a plan, partially diagrammatic, views of an alternative formof a bifurcated full-loop structure for supporting multiple electrodeelements having both a movable center ring and movable spline legs toextend and distend the bifurcated full-loop structure.

FIGS. 47, 48, and 49 are plan, partially diagrammatic, views of anotheralternative form of a bifurcated full-loop structure for supportingmultiple electrode elements having movable half-loop structures toextend and distend the bifurcated full-loop structure.

FIG. 50 is a plan view of a full-loop structure for supporting andguiding a movable electrode element.

FIG. 51 is a side elevation view of the full-loop structure and movableelectrode element shown in FIG. 50.

FIG. 52 is an enlarged view of the movable electrode supported andguided by the structure shown in FIG. 50, comprising wound coils wrappedabout a core body.

FIG. 53 is an enlarged view of another movable electrode that can besupported and guided by the structure shown in FIG. 50, comprisingbipolar pairs of electrodes.

FIG. 54 is a largely diagrammatic view of the full-loop structure andmovable electrode element shown in FIG. 50 in use within the atrium of aheart.

FIG. 55 is a perspective, elevation view of a bundled loop structure forsupporting multiple electrode elements, comprising an array ofindividual spline legs structures, each having a movable portion thatindependently extends and distends the individual structures to shapeand flex the overall bundled loop structure.

FIG. 56 is a top view of the bundled loop structure shown in FIG. 55.

FIG. 57 is a perspective elevation view of the bundled loop structureshown in FIG. 55 with some of the independently movable spline legsextended and distended to change the flexure of the bundled loopstructure.

FIG. 58 is a top view of the bundled loop structure shown in FIG. 57.

FIGS. 59a and 59 b are, respectively, top and side views of a bundledloop structure like that shown in FIG. 55 in position within an atrium,out of contact with the surrounding atrial wall.

FIGS. 60a and 60 b are, respectively, top and side views of a bundledloop structure like that shown in FIG. 57, with some of theindependently movable spline legs extended and distended to change theflexure of the bundled loop structure, to bring it into contact with thesurrounding atrial wall.

FIG. 61 is a top section view of the base of the bundled loop structureshown in FIG. 55.

FIG. 62 is a side, partial section view of a surgical device forpositioning an operative element within a patient in accordance with apreferred embodiment of one of the present inventions.

FIG. 63 is an end view of the surgical device shown in FIG. 62.

FIG. 64a is a side view of a surgical device for positioning anoperative element within a patient in accordance with another preferredembodiment of one of the present inventions.

FIG. 64b is a partial side view of a portion of the surgical deviceshown in FIG. 64a.

FIG. 65 is a side, partial section view of a portion of the surgicaldevice shown in FIG. 64a.

FIG. 66 is a side view of a surgical device for positioning an operativeelement within a patient in accordance with still another preferredembodiment of one of the present inventions.

FIG. 67a is a partial side, cutaway view of a surgical device forpositioning an operative element within a patient in accordance with yetanother preferred embodiment of one of the present inventions.

FIG. 67b is a section view taken along line 67 b—67 b in FIG. 67a.

FIG. 68 is a section view showing an operative element coated withregenerated cellulose.

FIG. 69a is a section view showing a partially masked operative element.

FIG. 69b is a section view showing an alternative operative elementconfiguration.

FIGS. 70a-70 c are front views of a spline assembly in accordance withan embodiment of one of the present inventions.

FIG. 70d is a side view of the spline assembly shown in FIGS. 70a-70 c.

FIG. 70e is a section view taken along line 70 e—70 e in FIG. 70a.

FIG. 70f is a partial front, partial section view of a surgical devicefor positioning an operative element within a patient in accordance withyet another preferred embodiment of one of the present inventions.

FIG. 71a is a side view of a surgical device for positioning anoperative element within a patient in accordance with a preferredembodiment of one of the present inventions.

FIG. 71b is a side, partial section view of an alternate tip that may beused in conjunction with the device shown in FIG. 71a.

FIG. 71c is a side, section view of another alternate tip that may beused in conjunction with the device shown in FIG. 71a.

FIG. 71d is a perspective view of a probe handle in accordance with apresent invention.

FIG. 71e is a perspective view of a probe handle in accordance withanother embodiment of present invention.

FIG. 71f is an exploded perspective view of a probe in accordance withone embodiment of a present invention.

FIG. 71g is an enlarged view of a portion of the probe shown in FIG.71f.

FIG. 71h is a plan view of an electrophysiology system in accordancewith one embodiment of a present invention.

FIG. 71i is an enlarged view of the remote power control unit shown inFIG. 71h.

FIG. 72a is a section view of the distal portion of the device shown inFIG. 71a taken along line 72 a—72 a in FIG. 71a.

FIG. 72b a section view of an alternate distal portion for the deviceshown in FIG. 71a.

FIG. 72c is a side, partial section view of another alternative distalportion for the device shown in FIG. 71a.

FIG. 73 is a section view taken along line 73—73 in FIG. 71a.

FIG. 74 is a side view of a surgical device for positioning an operativeelement within a patient in accordance with another preferred embodimentof one of the present inventions.

FIG. 75 is a side view of a surgical device for positioning an operativeelement within a patient in accordance with yet another preferredembodiment of one of the present inventions.

FIG. 76 is a perspective view of a portion of the device shown in FIG.75.

FIG. 77 is a side view of a surgical device for positioning an operativeelement within a patient in accordance with still another preferredembodiment of one of the present inventions.

FIG. 78 is a side view of a clamp in accordance with a preferredembodiment of one of the present inventions.

FIG. 79 is a section view taken along line 79—79 in FIG. 78.

FIG. 80 is a top view of the clamp illustrated in FIG. 78.

FIG. 81 is a side view of a surgical device for positioning an operativeelement within a patient and applying a clamping force to a bodilystructure in accordance with a preferred embodiment of one of thepresent inventions.

FIG. 82 is a side view of a surgical device for positioning an operativeelement within a patient and applying a clamping force to a bodilystructure in accordance with another preferred embodiment of one of thepresent inventions.

FIG. 83 is a side view of a surgical device for positioning an operativeelement within a patient and applying a clamping force to a bodilystructure in accordance with still another preferred embodiment of oneof the present inventions.

FIG. 84 is a top view of the operative element supporting member of thesurgical device shown in FIG. 83.

FIG. 85a is a top view of another operative element supporting member.

FIG. 85b is a top view of still another operative element supportingmember.

FIG. 86 is a side view of a surgical device for positioning an operativeelement within a patient and applying a clamping force to a bodilystructure in accordance with yet another preferred embodiment of one ofthe present invention.

FIG. 87 is a side, partial section view of an exemplary procedureinvolving the surgical device shown in FIG. 81.

FIG. 88 is a side, partial section view of an exemplary procedureinvolving a surgical device having an alternate support memberconfiguration.

FIGS. 89 and 90 are schematic views of a system for controlling theapplication of ablating energy to multiple electrodes using multipletemperature sensing inputs.

FIG. 91 is a schematic flow chart showing an implementation of thetemperature feedback controller shown in FIGS. 89 and 90, usingindividual amplitude control with collective duty cycle control.

FIG. 92 is a schematic view of a neural network predictor, whichreceives as input the temperatures sensed by multiple sensing elementsat a given electrode region and outputs a predicted temperature of thehottest tissue region.

FIG. 93 is a fragmentary side view showing the use of a grabbingcatheter in conjunction with a lasso catheter for maintaining the wallsof the inverted appendage together.

FIG. 94 is a fragmentary view of the combination shown in FIG. 93illustrating further steps of tying an appendage in an invertedorientation.

FIG. 95 is a perspective view of a pressure application probe inaccordance with a preferred embodiment of a present invention secured toan operative element supporting probe.

FIG. 96 is an enlarged perspective view of the pressure applicationprobe shown in FIG. 95.

FIG. 97 is a partial perspective view of a pressure application probe inaccordance with another preferred embodiment of a present invention.

FIG. 98 is a perspective view of a coupling device in accordance with apreferred embodiment of a present invention.

FIG. 99 is a perspective view showing a pressure application probe andthe coupling device shown in FIG. 98 being used in combination with thesurgical device shown in FIG. 71a.

FIG. 100 is a perspective view showing the coupling device shown in FIG.98 being used in combination with the surgical device shown in FIG. 71a.

FIG. 101 is a perspective view of a coupling device in accordance withanother preferred embodiment of a present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following is a detailed description of the best presently knownmodes of carrying out the inventions. This description is not to betaken in a limiting sense, but is made merely for the purpose ofillustrating the general principles of the inventions.

The detailed description of the preferred embodiments is organized asfollows:

I. Bi-Directional Flexible Structures

II. Probe-Type Apparatus

Ill. Operative Elements

IV. Epicardial Applications of Probe-Type Apparatus

V. Endocardial Applications of Probe-Type Apparatus

VI. Other Surgical Applications

VII. Apparatus that Apply a Clamping Force

VIII. Applications of Apparatus that Apply a Clamping Force

IX. Power Control

The section titles and overall organization of the present detaileddescription are for the purpose of convenience only and are not intendedto limit the present invention.

This specification discloses a number of electrode structures, mainly inthe context of cardiac ablation, because the structures are well suitedfor use with myocardial tissue. Nevertheless, it should be appreciatedthat the structures are applicable for use in therapies involving othertypes of soft tissue. For example, various aspects of the presentinventions have applications in procedures concerning other regions ofthe body such as the prostate, liver, brain, gall bladder, uterus andother solid organs.

I. Bi-Directional Flexible Structures

The exemplary structures, systems, and techniques illustrated in thisSection are discussed in the context of catheter-based cardiac ablation.Nevertheless, it should be appreciated that the structures, systems, andtechniques are applicable for use in other tissue ablation applications,including those that are not necessarily catheter-based.

A. Loop Support Structures for Multiple Electrodes

FIG. 1 shows a multiple electrode probe 10 that includes a loopstructure 20 carrying multiple electrode elements 28. Instead of, or inaddition to the electrode elements, the loop structure can carry one ormore of the other operative elements discussed in Section III below.

The probe 10 includes a flexible catheter tube 12 with a proximal end 14and a distal end 16. The proximal end 14 carries an attached handle 18.The distal end 16 carries a loop structure 20 that supports multipleelectrodes.

In FIG. 1, the loop support structure 20 comprises two flexible splinelegs 22 spaced diametrically opposite each other. The dual leg loopstructure 20 shown in FIG. 1 will be called a “full-loop” structure.

The far ends of the spline legs 22 radiate from a distal hub 24. Thenear ends of the spline legs 22 radiate from a base 26 attached to thedistal end 16 of the catheter tube 12. The multiple electrode elements28 are arranged along each spline leg 22.

In one implementation, the two spline legs 22 of the structure 20 arepaired together in an integral loop body 42 (see FIG. 2). Each body 42includes a mid-section 44 from which the spline elements 22 extend as anopposed pair of legs. As FIG. 2 shows, the mid-section 44 includes apreformed notch or detent 46, whose function will be described later.

The loop body 42 is preferably made from resilient, inert wire, likeNickel Titanium (commercially available as Nitinol material). However,resilient injection molded inert plastic or stainless steel can also beused. Preferably, the spline legs 22 comprise thin, rectilinear stripsof resilient metal or plastic material. Still, other cross sectionalconfigurations can be used.

In this implementation (see FIGS. 3 and 4), the distal hub 24 has agenerally cylindrical side wall 50 and a rounded end wall 52. Alongitudinal slot 56 extends through the hub 24, diametrically acrossthe center bore 54.

In the illustrated embodiment, the hub 24 is made of an inert, machinedmetal, like stainless steel. The bore 54 and slot 56 can be formed byconventional EDM techniques. Still, inert molded plastic materials canbe used to form the hub 24 and associated openings.

In this implementation, to assemble the structure 20 (see FIGS. 4 and5), a spline leg 22 of the hoop-like body 42 is inserted through theslot 56 until the mid-body section 44 enters the bore 54. The detent 46snaps into the bore 54 (see FIG. 4) to lock the body 42 to the hub 24,with the opposed pair of spline legs 22 on the body 42 radiating free ofthe slot 56 (see FIG. 5).

In the illustrated embodiment (see FIGS. 5 and 6a), the base 26 includesan anchor member 62 and a mating lock ring 64. The anchor member 62 fitswith an interference friction fit into the distal end 16 of the cathetertube 12. The lock ring 64 includes a series of circumferentially spacedgrooves 66 into which the free ends of the spline legs 22 fit. The lockring 64 fits about the anchor member 62 to capture with an interferencefit the free ends of the spline legs 22 between the interior surface ofthe grooves 66 and the outer surface of the anchor member 62 (see FIG.6). The anchor member 62/lock ring 64 assembly holds the spline elements22 in a desired flexed condition.

In an alternative construction (see FIG. 6b), the base 26 can comprise aslotted anchor 63 carried by the distal end 16 of the catheter tube 12.The slotted anchor 63 is made of an inert machined metal or moldedplastic material. The slotted anchor 63 includes an outer ring 65 and aconcentric slotted inner wall 67. The interior of the anchor 63 definesan open lumen 226 to accommodate passage of wires and the like betweenthe catheter tube bore 36 and the support structure 20 (as will bedescribed in greater detail later).

The inner wall 67 includes horizontal and vertical slots 69 and 71 forreceiving the free ends of the spline legs 22. The free ends passthrough the horizontal slots 69 and are doubled back upon themselves andwedged within the vertical slots 71 between the outer ring 65 and theinner wall 67, thereby securing the spline legs 22 to the anchor 63.

There are other alternative ways of securing the spline legs 22 to thedistal end 16 of the catheter tube 12, which will be described later.

Preferably, the full-loop structure 20 shown in FIG. 1 does not includea hub 24 like that shown in FIGS. 1 and 3, and, in addition, does notincorporate a detented integral loop body 42 like that shown in FIG. 2.Any single full-loop structure without a center stiffener or stylet (aswill be described later) preferably comprises a single length ofresilient inert wire (like Nickel Titanium) bent back upon itself andpreformed with resilient memory to form the desired full loop shape.Structure 112 in FIG. 29 (which will be described in greater detaillater) exemplifies the use of a preshaped doubled-back wire to form aloop, without the use of a hub 24 or detented loop body 42.

FIG. 7 shows an alternative loop structure 20(1) that includes a singlespline leg 22(1) carrying multiple electrode elements 28. This singleleg loop structure will be called a “half-loop” structure, in contrastto the dual leg loop structure 20 (i.e., the “full-loop structure) shownin FIG. 1.

In assembling the half-loop structure 20(1) shown in FIG. 7, thehoop-like body 42 shown in FIG. 2 is cut on one side of the detent 46 toform the single spline leg 22(1). The single spline leg 22(1) issnap-fitted into the hub 24 and captured with an interference fit by theanchor member 62/lock ring 64 assembly of the base 26 in the manner justdescribed (shown in FIGS. 5 and 6a). Alternatively, the single splineleg 22(1) can be wedged within the base anchor ring 63 shown in FIG. 6b.In FIG. 7, the half-loop structure 20(1) also includes a centerstiffener 40 passing through the base 26 and to the bore 54 of the hub24. The stiffener 40 can be made of a flexible plastic like PEEK, orfrom a hollow tube like hypo-tubing or braid plastic tubing.

It should be appreciated that other loop-type configurations besides thefull-loop structure 20 and half-loop structure 20(1) are possible. Forexample, two half-loop structures 20(1), one or both carrying electrodeelements 28, can be situated in circumferentially spaced apart positionswith a center stiffener 40, as FIG. 8 shows. As another example, fourhalf-loop structures, or two full-loop structures can be assembled toform a three-dimensional, basket-like structure 60 (without using acenter stiffener 40), like that shown in FIG. 9.

Regardless of the configuration, the loop structure provides theresilient support necessary to establish and maintain contact betweenthe electrode elements 28 and tissue within the body.

The electrode elements 28 can serve different purposes. For example, theelectrode elements 28 can be used to sense electrical events in hearttissue. In the illustrated and preferred embodiments, the principal useof the electrode elements 28 is to emit electrical energy to ablatetissue. In the preferred embodiments, the electrode elements 28 areconditioned to emit electromagnetic radio frequency energy.

As described in greater detail in Section III below, the electrodeelements 28 can be assembled in various ways.

In one preferred embodiment (see FIG. 10), the elements comprisemultiple, generally rigid ring electrode elements 30 arranged in aspaced apart, segmented relationship upon a flexible, electricallynonconductive sleeve 32 which surrounds the underlying spline leg 22.The sleeve 32 is made a polymeric, electrically nonconductive material,like polyethylene or polyurethane. The electrode rings 30 are pressurefated about the sleeve 32. The flexible portions of the sleeve 32between the rings 30 comprise electrically nonconductive regions.Alternatively, the electrode segments 30 can comprise a conductivematerial coated upon the sleeve 32. The electrode coating can be appliedeither as discrete, closely spaced segments or in a single elongatedsection.

In a more preferred embodiment (see FIGS. 11a and 11 b), spaced apartlengths of closely wound, spiral coils are wrapped about the sleeve 32to form an array of segmented, generally flexible electrodes 34. Theinherent flexible nature of a coiled electrode structures 34 also makespossible the construction of a continuous flexible ablating elementcomprising an elongated, closely wound, spiral coil wrapped about all ora substantial length of the flexible sleeve 32.

The electrode elements 28 can be present on all spline legs 22, as FIG.1 shows, or merely on a selected number of the spline legs 22, with theremaining spline legs serving to add structural strength and integrityto the structure.

Various access techniques can be used to introduce the probe 10 and itsloop support structure 20 into the desired region of the heart. Forexample, to enter the right atrium, the physician can direct the probe10 through a conventional vascular introducer through the femoral vein.For entry into the left atrium, the physician can direct the probe 10through a conventional vascular introducer retrograde through the aorticand mitral valves.

Alternatively, the physician can use the delivery system shown in U.S.Pat. No. 5,636,634 entitled “Systems and Methods Using Guide Sheaths forIntroducing, Deploying, and Stabilizing Cardiac Mapping and AblationProbes.”

In the illustrated and preferred embodiments (see FIGS. 10 and 11a/b),each flexible ablation element carries at least one and, preferably, atleast two, temperature sensing elements 68. The multiple temperaturesensing elements 68 measure temperatures along the length of theelectrode element 28. The temperature sensing elements 68, which cancomprise thermistors or thermocouples, can be located on the ablationelements in the manner shown in FIGS. 10 and 11a/b. Preferably, thetemperature sensing elements 68 can be located on one or both of thelongitudinal end edges of the ablation elements, as shown in U.S. patentapplication Ser. No. 08/788,782, entitled “Systems and Methods forControlling Ablation Using Multiple Temperature Sensing Elements,” whichis incorporated herein by reference.

An external temperature processing element, such as that discussed belowin Section IX, receives and analyses the signals from the multipletemperature sensing elements 68 in prescribed ways to govern theapplication of ablating energy to the flexible ablation element. Theablating energy is applied to maintain generally uniform temperatureconditions along the length of the element. Additionally, furtherdetails of the use of multiple temperature sensing elements in tissueablation can be found in co-pending U.S. application Ser. No.08/638,989, filed Apr. 24, 1996, which is File Wrapper Continuation ofU.S. application Ser. No. 08/286,930, filed Aug. 8, 1994, entitled“Systems and Methods for Controlling Tissue Ablation Using MultipleTemperature Sensing Elements.”

To aid in locating the structure 20 within the body, the handle 16 andcatheter body 12 preferably carry a steering mechanism 70 (see FIGS. 1and 12) for selectively bending or flexing the distal end 16 of thecatheter body 12.

The steering mechanism 18 can vary. In the illustrated embodiment (seeFIG. 12), the steering mechanism 70 includes a rotating cam wheel 72with an external steering lever 74 (see FIG. 1). As FIG. 12 shows, thecam wheel 72 holds the proximal ends of right and left steering wires76. The steering wires 76, like the signal wires 58, pass through thecatheter body lumen 36. The steering wires 76 connect to the left andright sides of a resilient bendable wire or spring (not shown) enclosedwithin the distal end 16 of the catheter body 12. Forward movement ofthe steering lever 74 flexes or curves the distal end 16 down. Rearwardmovement of the steering lever 74 flexes or curves the distal end 16 up.

Further details of this and other types of steering mechanisms are shownin Lundquist and Thompson U.S. Pat. No. 5,254,088, which is incorporatedinto this Specification by reference.

B. Variable Shape Loop Support Structures

To uniformly create long, thin lesions having the desired therapeuticeffect, the loop support structure 20 or 20(1) must make and maintainintimate contact between the electrode elements 28 and the endocardium.This invention provides loop support structures that the physician canadjust to adapt to differing physiologic environments.

1. Distended Loop Structures

The adjustable loop structure 78 shown in FIG. 13 is in many respectssimilar to the full-loop structure 20 shown in FIG. 1. The adjustablefull-loop structure 78 includes the pair of diametrically oppositespline legs 22 that radiate from the base 26 and hub 24.

In addition, the adjustable full-loop structure 78 includes a flexiblestylet 80 attached at its distal end to the hub bore 54. The stylet 80can be made from a flexible plastic material, like PEEK, or from ahollow tube, like hypo-tubing or braid plastic tubing.

The stylet 80 extends along the axis of the structure 78, through thebase 26 and catheter body lumen 36, and into the handle 18. In thisarrangement, the stylet 80 is free to slide fore and aft along the axisof the catheter body 12.

The proximal end of the stylet 80 attaches to a control knob 82 in thehandle 18 (as FIG. 13 shows). The control knob 82 moves within a groove84 (see FIGS. 13 and 14) in the handle 18 to impart fore and aftmovement to the stylet 80. Stylet movement changes the flexure of thestructure 78.

Forward movement of the stylet 80 (i.e., toward the distal end 16)pushes the hub 24 away from the base 26 (see FIG. 15). The loopstructure 78 elongates as the spline legs 22 straighten and moveradially inward, to the extent permitted by the resilience of the splinelegs 22. With the spline legs 22 straightened, the loop structure 78presents a relatively compact profile to facilitate vascularintroduction.

Rearward movement of the stylet 80 (i.e., toward the distal end 16)pulls the hub 24 toward the base 26 (see FIG. 16). The spline legs 22bend inward in the vicinity of the hub 24, while the remainder of thesplines, constrained by the base, distend. The loop structure 78 bowsradially out to assume what can be called a “heart” shape.

When the structure 78 is positioned within the atrium 88 of a heart inthe condition shown in FIG. 16, the stylet 80 compresses the spline legs22, making them expand or bow radially. The expansion presses thedistended midportion of the spline legs 22 (and the electrode elements28 they carry) symmetrically against opposite walls 86 of the atrium 88.The symmetric expansion of the outwardly bowed spline legs 22 pressesthe opposite atrial walls 86 apart (as FIG. 16 shows), as the radialdimension of the loop structure 78 expands to span the atrium 88.

The symmetric expansion presses the electrode elements 28 into intimatesurface contact against the endocardium. The symmetric expansionstabilizes the position of the loop structure 78 within the atrium 88.The resilience of the spline legs 22, further compressed by thepulled-back stylet 80, maintains intimate contact between the electrodeelements 28 and atrial tissue, without trauma, as the heart expands andcontracts.

As FIGS. 17 to 19 show, the push-pull stylet 80 can also be used inassociation with a half-loop structure 90, like that previously shownand discussed in FIG. 7.

In this arrangement, pushing the stylet 80 forward (as FIG. 18 shows)elongates the half-loop structure 90 for vascular introduction. Pullingthe stylet 80 rearward (as FIG. 19 shows) bows the single spline leg 22of the structure outward, expanding it so that more secure contact canbe achieved against the atrial wall 86, or wherever tissue contact isdesired.

2. Curvilinear Loop Structures

FIGS. 20 and 21 show a full-loop structure 92 that includes a centerstylet 94, which can be flexed. The flexing of the center stylet 94bends the spline legs 22 in a second direction different than the radialdirection in which they are normally flexed. In the illustratedembodiment, this second direction is generally perpendicular to the axesof the spline legs 22, as FIGS. 23a/b and 24 show, although acute bendsthat are not generally perpendicular can also be made. The bending ofthe spline legs 22 in this fashion makes possible the formation of long,thin curvilinear lesions using a full-loop structure 92, or (as will bedescribed later) in a half-loop structure 110, as well.

The stylet 94 itself can be either fixed in position between the hub 24and the base 26, or movable along the axis of the loop structure 92 toextend and distend the radial dimensions of the spline legs 22 in themanner already described (see FIGS. 15 and 16). In the illustrated andpreferred embodiment, the stylet 94 slides to alter the radialdimensions of the structure.

In one implementation, as FIG. 22 best shows, the stylet 94 is made froma metal material, for example stainless steel 17-7, Elgiloy™ material,or Nickel Titanium material. A pair of left and right steering wires,respectively 96(R) and 96(L) is attached to opposite side surfaces ofthe stylet 94 near the hub 24, by adhesive, soldering, or by suitablemechanical means. The steering wires 96(R) and 96(L) are attached to thestylet side surfaces in a diametric opposite orientation that is atright angles to the radial orientation of the spline legs 22 relative tothe stylet 94.

The steering wires 96(R) and 96(L) extend along the stylet 94, throughthe base 26 and catheter body lumen 36, and into the handle 18 (see FIG.25). Preferably, as FIG. 22 best shows, a tube 98 surrounds the stylet94 and steering wires 96(R) and 96(L), at least along the distal,exposed part of the stylet 94 within the structure 92, keeping them in aclose relationship. The tube 98 can be heat shrunk to fit closely aboutthe stylet 94 and steering wires 96(R) and 96(L).

As FIGS. 25 and 26 show, a groove 100 in the handle carries a controlassembly 102. The stylet 94 is attached to the control assembly 102, inthe manner already described with respect to the control knob 82 inFIGS. 13 and 14. Sliding movement of the control assembly 102 within thegroove 100 imparts fore and aft movement to the stylet 94, therebydistending or extending the loop structure 92.

The control assembly 102 further includes a cam wheel 104 (see FIG. 26)rotatable about an axle on the control assembly 102 in response to forceapplied to an external steering lever 108. The cam wheel 104 holds theproximal ends of the steering wires 96(R) and 96(L), in the mannerdisclosed in Lundquist and Thompson U.S. Pat. No. 5,254,088, alreadydiscussed, which is incorporated herein by reference.

Twisting the steering lever 108 counterclockwise applies tension to theleft steering wire 96(L), bending the loop structure 92 to the left (asFIG. 23a shows). The electrode elements 28 (which in FIGS. 20 to 27comprises a continuous coil electrode 34, described earlier) likewisebend to the left.

Similarly, twisting the steering lever 108 clockwise applies tension tothe right steering wire 96(R), bending the loop structure 92 to theright (as FIGS. 23b and 24 show). The electrode elements 28 likewisebend to the right.

The bent electrode elements 28, conforming to the bent spline legs 22,assume different curvilinear shapes, depending upon amount of tensionapplied by the steering wires 96(R) and 96(L). When contacting tissue,the bent electrode elements 28 form long, thin lesions in curvilinearpatterns.

In an alternative implementation, the stylet 94 is instead made of amalleable metal material, like annealed stainless steel. In thisarrangement, before deployment in the body, the physician appliesexternal pressure to manually bend the stylet 94 into a desired shape,thereby imparting a desired curvilinear shape to the electrode elementsof the associated loop structure. The malleable material of the stylet94 retains the preformed shape, until the associated loop structure iswithdrawn from the body and sufficient external pressure is againapplied by the physician to alter the stylet shape.

In addition to having a malleable stylet 94, the splines 22 themselvescan also be made of a malleable material, like annealed stainless steel,or untreated stainless steel 17-7, or untreated Nickel Titanium. In oneimplementation, the most distal parts of the malleable splines 22 areheat treated to maintain their shape and not collapse duringintroduction and deployment in the vascular system. This will also givethe overall structure greater stiffness for better contact with thetissue. It also gives the physician the opportunity to bend thestructure to form long, thin, lesions in prescribed curvilinear patternsset by the malleable splines.

Whether flexible and remotely flexed during deployment, or malleable andmanually flexed before deployment, by further adjusting the fore-and-aftposition of the stylet 94, the physician can also control the radialdimensions of the loop structure 94 in concert with controlling thecurvilinear shape of the loop structure 92, as FIG. 27 shows. A diversearray of radial sizes and curvilinear shapes is thereby available.

As FIG. 28 shows, a half-loop structure 110 can also include a fixed ormovable stylet 94 with steering wires 96(R) and 96(L). The use of thesame handle-mounted control assembly 102/rotatable cam 104 assemblyshown in FIGS. 25 and 26 in association with the half-loop structure 110makes possible the creation of diverse curvilinear shapes of variableradii. Alternatively, a malleable stylet 94 and malleable splines can beused.

3. Loop Structures with Movable Spline Legs

FIGS. 29 to 35 show a full-loop structure 112 in which only one splineleg 114 is attached to the base 26. The fixed spline leg 114 ispreformed with resilient memory to assume a curve of a selected maximumradius (shown in FIG. 33). The other spline leg 116, locateddiametrically opposed to the fixed spline leg 114, extends through thebase 26 and catheter body lumen 36 (see FIGS. 30a and 30 b) into thehandle 18. The spline leg 116 slides fore and aft with respect to thebase 26. Movement of the spline leg 116 changes the flexure of thestructure 112.

The full-loop structure 112 shown in FIGS. 29 to 35 need not include ahub 24 like that shown in FIGS. 1 and 3, and, in addition, need notincorporate a detented integral loop body 42 like that shown in FIG. 2.Any single full-loop structure without a center stiffener or stylet,like the structure 112 in FIG. 29, can comprise a single length of wirebent back upon itself and preformed with resilient memory to form thedesired full loop shape. For the same reason, the single full-loopstructure 20 shown in FIG. 1 can, in an alternative construction, bemade without a hub 24 and a detented loop body 42, and instead employ apreshaped doubled-back wire to form a loop, like the structure 20.

FIG. 30b shows an alternative way of securing the fixed spline leg 114to the distal end 16 of the catheter tube 12, without using a base 26.In this embodiment, the free end of the fixed spline leg 114 liesagainst the interior of the tube 12. The leg 114 passes through a slit115 formed in the catheter tube 12. The leg 114 is bent back upon itselfin a u-shape to lie against the exterior of the tube 12, wedging thetube 12 within the u-shape bend 117. A sleeve 119 is heat shrunk aboutthe exterior of the tube 12 over the region where the u-shape bend 117of the spline leg 114 lies, securing it to the tube 12. Alternatively, ametallic ring (not shown) can be used to secure the spline leg 114 tothe tube 12. The movable spline leg 116 and wires 58 pass through theinterior bore 36 of the catheter tube 12, as before described.

The proximal end of the spline leg 116 (see FIG. 29) is attached to amovable control knob 82 carried in a groove 84 on the handle 18, likethat shown in FIG. 13. Movement of the control knob 82 within the groove84 thereby imparts fore-and-aft movement to the spline leg 116.

In the illustrated embodiment, the fixed spline leg 114 carrieselectrode elements 28 in the manner already described. The movablespline leg 116 is free of electrode elements 28. Still, it should beappreciated that the movable spline leg 116 could carry one or moreelectrode elements 28, too.

As FIGS. 31 to 33 show, moving the control knob 82 forward slides themovable spline leg 116 outward, and vice versa. The movable spline leg116 applies a counter force against the resilient memory of the fixedspline leg 114, changing the flexure and shape of the loop structure 112for vascular introduction and deployment in contact with tissue. Bypulling the movable spline leg 116 inward (as FIG. 31 shows), thecounter force contracts the radius of curvature of the fixed spline leg114 against its resilient memory. Pushing the movable spline leg 116outward (as FIGS. 32 and 33 show) allows the resilient memory of thefixed spline leg 114 to expand the radius of curvature until theselected maximum radius is achieved. The counter force applied changesthe flexure and shapes the fixed spline leg 114 and the electrodeelements 28 it carries to establish and maintain more secure, intimatecontact against atrial tissue.

The magnitude (designated V in FIGS. 31 to 33) of the counter force, andthe resulting flexure and shape of the loop structure 112, variesaccording to extent of outward extension of the movable spline leg 116.Pulling the movable spline leg 116 progressively inward (therebyshortening its exposed length) (as FIG. 31 shows) contracts the loopstructure 112, lessening its diameter and directing the counter forceprogressively toward the distal end of the structure. Pushing themovable spline leg 116 progressively outward (thereby lengthening itsexposed length) (as FIGS. 32 and 33 show) progressively expands the loopstructure 112 in response to the resilient memory of the fixed splineleg 114, increasing its diameter and directing the counter forceprogressively away from the distal end of the structure.

As FIGS. 34 and 35 show, by manipulating the movable spline leg 116, thephysician can adjust the flexure and shape of the loop structure 112within the atrium 88 from one that fails to make sufficient surfacecontact between the electrode element 28 and the atrial wall 86 (as FIG.34 shows) to one that creates an extended region of surface contact withthe atrial wall 86 (as FIG. 35 shows).

FIGS. 36 to 38 show a full-loop structure 118 in which each spline leg120 and 122 is independently movable fore and aft with respect to thebase 26. In the illustrated embodiment, both spline legs 120 and 122carry electrode elements 28 in the manner already described.

In this arrangement, the handle 18 includes two independently operable,sliding control knobs 124 and 126 (shown diagrammatically in FIGS. 36 to38), each one attached to a movable spline leg 120/122, to impartindependent movement to the spline legs 120/122 (as shown by arrows inFIGS. 36 to 38). Each spline leg 120/122 is preformed with resilientmemory to achieve a desired radius of curvature, thereby imparting aresilient curvature or shape to the full-loop structure 118 itself.Coordinated opposed movement of both spline legs 120/122 (as FIGS. 37and 38 show) using the control knobs 124/126 allows the physician toelongate the curvature of the loop structure 118 into more of an ovalshape, compared to more circular loop structures 112 formed using asingle movable leg 116, as FIGS. 31 to 33 show.

FIGS. 39a and 39 b show an alternative full-loop structure 128 havingone spline leg 130 that is fixed to the base 26 and another spline leg132, located diametrically opposed to the fixed spline 130, that ismovable fore and aft with respect to the base 26 in the manner alreadydescribed. The movable spline leg 132 can carry electrode elements 28(as FIG. 39a shows), or be free of electrode elements, depending uponthe preference of the physician.

In the structure shown in FIGS. 39a and 39 b, the fixed spline leg 130branches in its midportion to form a smaller, secondary full-loopstructure 134 that carries electrode elements 28. In the embodimentshown in FIGS. 39a and 39 b, the secondary loop structure 134 lies in aplane that is generally perpendicular to the plane of the main full-loopstructure 128.

The smaller, secondary full-loop structure 134 makes possible theformation of annular or circumferential lesion patterns encircling, forexample, accessory pathways, atrial appendages, and the pulmonary veinwithin the heart. In the illustrated embodiment, the movable spline leg132 compresses the secondary full-loop structure 134, urging andmaintaining it in intimate contact with the targeted tissue area.

FIGS. 39a and 39 b therefore show a compound flexible support forelectrode elements. While the primary support structure 128 and thesecondary support structure 134 are shown as full loops, it should beappreciated that other arcuate or non-arcuate shapes can be incorporatedinto a compound structure. The compound primary structure 128 integratedwith a secondary structure 134 need not include a movable spline leg,or, if desired, both spline legs can be movable. Furthermore, a centerstylet to contract and distend the main structure 128 can also beincorporated, with or without a stylet steering mechanism.

FIGS. 40a and 40 b show a modified full-loop structure 216 having an oddnumber of spline legs 218, 220, and 222. The structure 216 includes twospline legs 218 and 220 that, in the illustrated embodiment, are fixedto the base 26 about 1200 apart from each other. As FIG. 40b shows, thebase 26 is generally like that shown in FIG. 6b, with the slotted anchor63 in which the near ends of the legs 218 and 220 are doubled back andwedged. The structure 216 also includes a third spline leg 222 that, inthe illustrated embodiment, is spaced about 120° from the fixed splinelegs 218/220. As FIG. 40b shows, the near end of the third spline leg222 is not attached to the base 26, but passes through the inner lumen226 into the lumen 36 of the catheter tube 12. The third spline leg 222is thereby movable fore and aft with respect to the base 26 in themanner already described. Alternatively, all spline legs 218, 220, and222 can be fixed to the base 26, or more than one spline leg can be mademoveable.

A hub 24 like that shown in FIGS. 3 and 4 includes circumferentiallyspaced slots 56 to accommodate the attachment of the three splines 218,220, and 222.

The fixed splines 218 and 220 carry electrode elements 28 (as FIG. 40ashows), while the movable spline 22 is free of electrode elements. AsFIG. 40b show, the wires 58 coupled to the electrode elements 28 passthrough the anchor lumen 226 for transit through the catheter tube bore36. The orientation of the fixed splines 218 and 220 relative to themovable spline 222 thereby presents an ablation loop 224, like thesecondary loop structure 134 shown in FIGS. 39a/b, that lies in a planethat is generally transverse of the plane of the movable spline 222. Ofcourse, other orientations of an odd number of three or more spline legscan be used.

The movable spline leg 222 extends and compresses the secondarystructure 134 to urge and maintain it in intimate contact with thetargeted tissue area. Of course, a center stylet to further contract anddistend the ablation loop 224 can also be incorporated, with or withouta stylet steering mechanism.

4. Bifurcated Loop Structures

FIGS. 41, 42, and 43 show a variation of a loop structure, which will becalled a bifurcated full-loop structure 136. The structure 136 (see FIG.41) includes two oppositely spaced splines legs 138 and 140, eachcarrying one or more electrode elements 28. The near end of each splineleg 138/140 is attached to the base 26. The far end of each spline leg138/140 is attached a stylet 142 and 144. Each spline leg 138/140 ispreformed with resilient memory to achieve a desired maximum radius ofcurvature (which FIG. 41 shows).

The spline leg stylets 142/144 are joined through a junction 146 to acommon control stylet 148. The common control stylet 148 passes throughthe catheter body lumen 36 to a suitable slidable control knob 150 inthe handle 18, as already described. By sliding, the control knob 150moves the control stylet 148 to change the flexure of the spline legs138/140.

When the control stylet 148 is fully withdrawn, as FIG. 41 shows, thejunction 146 is located near the base 26 of the structure 136, and thespline legs 138/140 assume their preformed maximum radii of curvatures.The spline legs 138/140 form individual half-loop structures (like shownin FIG. 7) that together emulate a full-loop structure (like that shownin FIG. 1), except for the presence of a connecting, distal hub 24.

Forward movement of the control stylet 148 first moves the junction 146within the confines of the structure 136, as FIG. 42 shows. The forwardmovement of the control stylet 148 is translated by the spline legstylets 142/144 to urge the spline legs 138/140 apart. The distal end ofthe bifurcated structure 136 opens like a clam shell.

As the spline legs 138/140 separate, they distend. The control stylet150 thus compresses the splines legs 138/140 to press them into contactwith the tissue area along opposite sides of the structure 136. In thisway, the bifurcated structure 136 emulates the full-loop structure 78,when distended (as FIG. 16 shows).

Continued forward movement of the control stylet 150 (as FIG. 43 shows)moves the junction 146 and attached spline leg stylets 142/146 outbeyond the confines of the structure 136. This continued forwardmovement extends the spline legs 136/140, while moving them radiallyinward. This, in effect, collapses the bifurcated structure 136 into arelatively low profile configuration for vascular introduction. In thisway, the bifurcated structure 136 emulates the full-loop structure 78,when elongated (as FIG. 15 shows).

FIGS. 44 and 45 show an alternative embodiment of a bifurcated full-loopstructure 152. The structure 152 includes two oppositely spaced splinelegs 154/156, each carrying one or more electrode elements 28, like thestructure 136 shown in FIGS. 41 to 43. Each spline leg 154/156 ispreformed with a resilient memory to assume a desired maximum radius ofcurvature (which FIG. 44 shows).

Unlike the structure 136 shown in FIGS. 41 to 43, the structure 152shown in FIGS. 44 and 45 fixes both ends of the spline legs 154/156 tothe base 26. The spline legs 154/156 thereby form stationary,side-by-side half-loop structures, each with an inner portion 158 and anouter portion 160. Together, the stationary half-loop structures createthe bifurcated full-loop structure 152.

In this arrangement, a center stylet 162 is attached to a ring 164 thatcommonly encircles the inner portions 158 of the spline legs 154/156along the center of the structure 152. Movement of the stylet 162 slidesthe ring 164 along the inner leg portions 158. The stylet 162 passesthrough the catheter body lumen 36 to a suitable control in the handle(not shown), as already described.

Forward movement of the ring 164 (as FIG. 45 shows) jointly extends thespline legs 154/156, creating a low profile for vascular introduction.Rearward movement of the ring 164 (as FIG. 44 shows) allows theresilient memory of the preformed spline legs 154/156 to bow the legs154/156 outward into the desired loop shape.

FIG. 46 shows another alternative embodiment of a bifurcated full-loopstructure 166. This structure 166 has two oppositely spaced spline legs168 and 170, each carrying one or more electrode elements 28. Eachspline leg 168/170 is preformed with a resilient memory to assume amaximum radius of curvature (which FIG. 46 shows).

The near end of each spline leg 168/170 is attached to the base 26. Thefar end of each spline leg 168/170 is individually attached to its ownstylet 172/174. Instead of joining a common junction (as in thestructure 136 shown in FIGS. 41 to 43), the spline stylets 172/174 ofthe structure 166 individually pass through the catheter body lumen 36to suitable control knobs (not shown) in the handle 18. Like theembodiment shown in FIGS. 44 and 45, a third stylet 176 is attached to aring 178 that encircles the spline stylets 172 and 174. The third stylet176 passes through the guide tube lumen 36 to its own suitable controlknob (not shown) in the handle 18.

The embodiment shown in FIG. 46 allows the physician to move the ring178 up and down along the spline stylets 172 and 174 to shape and changethe flexure of the structure 166 in the manner shown in FIGS. 44 and 45.Independent of this, the physician can also individually move the splinestylets 172 and 174 to further shape and change the flexure of eachspline leg 168 and 170, as in the case of the movable spline legs120/122 shown in FIGS. 36 to 38. This structure 166 thus gives thephysician latitude in shaping the loop structure to achieve the desiredcontact with the atrial wall.

Another alternative embodiment of a bifurcated full-loop structure 180is shown in FIGS. 47 to 49. In this embodiment, the structure 180includes two oppositely spaced spline legs 182 and 184, each carryingone or more electrode elements 28. Each spline leg 182/184 is preformedwith a resilient memory to assume a desired maximum radius of curvature(which FIG. 49 shows).

The inner portion 186 of each spline leg 182/184 is attached to the base26. A stationary ring 190 encircles the inner portions 186 near thedistal end of the structure 180, holding them together.

The outer portion 188 of each spline leg 182/184 is free of attachmentto the base 26 and is resiliently biased away from the base 26. Eachouter portion 188 is individually attached to its own stylet 192 and194. The spline stylets 192 and 194 individually pass through thecatheter body lumen 36 to suitable control knobs (not shown) in thehandle 18.

Pulling the spline legs stylets 192/194 rearward pulls the outer portion188 of the attached spline leg 182/184 radially toward the base 26,against their resilient memories, creating a low profile suitable forvascular access (as FIG. 47 shows). Pushing the spline stylets 192/194forward pushes the outer portion 188 of the attached spline leg 182/184,aided by the resilient memory of the spline leg 182/184, outward (asFIGS. 48 and 49 show). The spline stylets 192/194 can be manipulatedtogether or individually to achieve the shape and flexure desired.

5. Loop Support Structures for Movable Electrodes

FIGS. 50 and 51 show a full-loop structure 196 which supports a movableablation element 198. The structure 196 includes a pair of spline legs200 secured at their distal ends to the hub 24 and at their proximalends to the base 26, in the manner described in association with thestructure shown in FIG. 1. A center stiffener 202 extends between thebase 26 and the hub 24 to lend further strength.

The ablation element 198 (see FIG. 52) comprises a core body 204 made ofan electrically insulating material. The body 204 includes a centrallumen 206, through which one of the spline legs 200 passes. The corebody 204 slides along the spline leg 200 (as shown by arrows in FIGS. 50to 52).

In the illustrated and preferred embodiment (see FIG. 52), a coilelectrode element 34 (as already described) is wound about the core body204. Alternatively, the core body 204 can be coated with an electricallyconducting material or have an electrically conducting metal bandfastened to it. As shown in FIG. 53, the ablation element can alsocomprise a composite structure 198(1) (see FIG. 53) of two bi-polarelectrodes 208 separated by an electrically insulating material 210. Thecore body 204 of the electrode can range in diameter from 3 Fr to 8 Frand in length from 3 mm to 10 mm.

A guide wire 212 is attached to at least one end of the ablationelectrode 198 (see FIGS. 50 and 52). The guide wire 212 extends from thehandle 18 through the catheter body lumen 36, along the center stiffener202 and through the hub 24 for attachment to the ablation element 198. Asignal wire 214 also extends in common along the guide wire 212 (seeFIG. 52) to supply ablation energy to the electrode 198. The proximalend of the guide wire 212 is attached to a suitable control knob (notshown) in the handle 18. Movement of the guide wire 212 forward pushesthe ablation element 198 along the spline leg 200 from the distal end ofthe structure 196 to the proximal end.

Two guide wires (212 and 213) may be used (as FIG. 52 shows), which areattached to opposite ends of the ablation element 198. Pulling on oneguide wire 212 advances the electrode 198 toward the distal end of thestructure 196, while pulling on the other guide wire 213 advances theelectrode 198 in the opposite direction toward the proximal end of thestructure 196. In an alternative implementation (not shown), the distaltip of a second catheter body can be detachably coupled eithermagnetically or mechanically to the movable electrode 198. In thisimplementation, the physician manipulates the distal end of the secondcatheter body into attachment with the electrode 198, and then uses thesecond catheter body to drag the electrode 198 along the structure 196.

In use (as FIG. 54 shows), once satisfactory contact has beenestablished with the atrial wall 86, sliding the ablation electrode 198along the spline leg 200 while applying ablation energy creates a longand thin lesion pattern. The ablation can be accomplished by eithermoving the electrode 198 sequentially to closely spaced locations andmaking a single lesion at each location, or by making one continuouslesion by dragging the electrode 198 along the tissue while ablating.

One or both spline legs 200 can also be movable with respect to thebase, as before described, to assure intimate contact between theablation element 198 and the endocardium.

6. Bundled Loop Structures

The assembly of bundled, independently adjustable loop structures toform a dynamic three dimensional electrode support structure 228, likethat shown in FIGS. 55 to 58, are also possible.

The structure 228 shown in FIGS. 55 to 58 comprises four spline legs(designated L1, L2, L3, and L4) circumferentially spaced ninety degreesapart. Each spline leg L1, L2, L3, and L4 is generally like that shownin FIG. 29. Each leg L1, L2, L3, and L4 is preformed with resilientmemory to assume a curve of selected maximum radius. In the illustratedembodiment, each leg L1 to L4 carries at least one electrode element 28,although one or more of the legs L1 to L4 could be free of electrodeelements 28.

The outer portions 230 of each spline leg L1 to L4 are attached to thestructure base 26. As FIG. 61 shows, the base 26 is similar to thatshown in FIG. 30b, having an outer ring 236 and a concentric slottedinner element 238, through which the near ends of the outer spline legportions 230 extend. The near ends are doubled back upon themselves andwedged in the space 240 between the outer ring 236 and inner element238, as earlier shown in FIG. 6b.

The inner portions 232 of each spline leg L1, L2, L3, and L4 are notattached to the base 26. They pass through lumens 242 in the innerelement 238 of the base 26 (see FIG. 61) and into catheter body lumen 36for individual attachment to control knobs 234 on the handle 18 (seeFIG. 55). Wires 58 associated with the electrode elements 28 carried byeach leg L1 to L4 pass through other lumens 244 in the inner element 238(see FIG. 61).

The inner portion 232 of each spline leg L1 to L4 is independentlymovable, in the same way as the spline leg shown in FIGS. 31 to 35. Bymanipulating the control knobs 234, the physician can change the normalflexure of the structure 228 (which FIGS. 55 and 56 show) to a newflexure (which FIGS. 57 and 58 show), by altering the shape each splineleg L1 to L4 independent of each other. As FIGS. 57 and 58 show, theinner portion 232 of leg L4 has been pulled aft, compressing theassociated loop. The inner portion 232 of leg L2 has been pushedforward, expanding the associated loop.

As FIGS. 59a/b and 60 a/b show, by selective manipulation of the movableinner portions 232 of the spline legs L1 to L4, the physician can adjustthe shape of the three dimensional loop structure 228 within the atrium88 from one that fails to make sufficient surface contact between theelectrode element 28 and the atrial wall 86 (as FIGS. 59a/b show) to onethat expands the atrium 88 and creates an extended region of surfacecontact with the atrial wall 86 (as FIGS. 60a/60 b show). The physiciancan thereby tailor the shape of the three dimensional structure 228 tothe particular physiology of the patient.

In an alternative arrangement, the inner portions 232 of the spline legsL1 to L4 can be fixed to the base 26 and the outer portions 230 madefree to move in the manner shown in FIGS. 47 to 49.

C. Conclusion

It should be now be apparent that one or more movable spline legs can beused in association with a movable center stylet to provide control ofthe shape and flexure of the ablation element. The further inclusion ofsteering wires on the movable stylet, or the use of a malleable styletand/or malleable spline legs adds the ability to form curvilinear lesionpatterns.

It is thereby possible to combine in a single loop support structure oneor more movable spline legs (as FIGS. 31 to 38 show), a movable centerstylet (as FIGS. 13 to 19 show), and a stylet steering assembly ormalleable stylet/splines (as FIGS. 20 to 28 show). Such a structure iscapable of creating a diverse number of shapes and contact forces toreliably achieve the type and degree of contact desired between theablation elements and the targeted tissue area, despite physiologicdifferences among patients.

It should also be appreciated that the inventions discussed in thissection are applicable for use in tissue ablation applications that arenot catheter-based. For example, any of the loop structures like thosedescribed herein can be mounted at the end of hand-held probe for directplacement by the physician in contact with a targeted tissue area. Forexample, a hand held loop structure carrying multiple electrodes can bemanipulated by a physician to ablate tissue during open heart surgeryfor mitral valve replacement.

II. Probe-Type Apparatus

As illustrated for example in FIGS. 62 and 63, a surgical device (or“probe”) 250 for positioning an operative element 252 within a patientincludes a relatively short shaft 254 and a bendable spline assembly256, associated with the distal end of the shaft, for supporting theoperative element. Here, the operative element 252 is in the form of aplurality of electrode elements 294, as discussed in greater detail inSection III below. Preferably, the relatively short shaft may be betweenapproximately 4 and 18 inches in length, and is preferably 8 inches inlong, while the outer diameter of the shaft is preferably betweenapproximately 6 and 24 French. The spline assembly 256 has apredetermined use configuration. In the exemplary embodiment shown inFIGS. 62 and 63, the spline assembly includes a pair of spline legs 258and 260 and an annular member 262 which supports the operative element252. The surgical device also includes a tubular member 264 (acylindrically shaped sheath in the exemplary embodiment) which covers aportion of the shaft 254 and is also slidable relative thereto. Thespline assembly 256 is adapted to collapse (the insertion configuration)in response to movement of the substantially tubular member 264 in thedistal direction and to expand to the predetermined use configurationwhen the substantially tubular member is moved in the proximaldirection. A handle 266 may be provided on the proximal end of the shaft254. The tubular member 264 preferably includes a raised grippingsurface 268.

Another exemplary surgical device (or “probe”) for positioning anoperative element within a patient, which is generally represented byreference numeral 270, is illustrated in FIGS. 64a-65. Here, thesurgical device includes a substantially triangularly shaped splineassembly 272 that consists of first and second side legs 274 and 276 anda distal leg 278. The distal leg 278, which is preferably non-linearfrom end to end and approximately 10 to 12 cm in length, includes firstand second linear portions 280 and 282 and a bent portion 284 locatedmid-way between the ends. This spline configuration provides a springforce against the selected bodily surface during use (such as the atriumwall in a cardiac procedure) and the bend in the distal leg 278optimizes the contact between the operative element 252 and the selectedsurface. The spline assembly 272 will collapse in the manner shown inFIG. 65 when the tubular member 264 is advanced thereover and willreturn to the orientation shown in FIG. 64a when the tubular member isretracted. The surgical device 270 also includes a second handle 267.

During use of the exemplary surgical device shown in FIGS. 62-65, thehandle 266 (FIG. 62) or 267 (FIG. 64a) is grasped by the physician andforce is applied through the shaft 254 and side legs 258 and 260 (FIG.62) or 274 and 276 (FIG. 64a) to the operative element supportingannular member 262 (FIG. 62) or distal leg 278 (FIG. 64a). Thus, theshaft and side legs (including the area where the side legs meet) shouldbe sufficiently strong to prevent collapse when the force is applied.The fact that the present devices are not passed through a torturedvascular path to the site of interest allows the shaft and spline legsto be stiffer than a conventional catheter shaft. This aspect of theinvention is discussed in greater detail below. Alternatively, the shaft254 and side legs 274 and 276 in the embodiment shown in FIGS. 64a and65 may be configured such that they collapse and form a semicircle withthe distal leg 278 when force is applied to the shaft (note FIG. 64b).Here, the operative element should be appropriately masked in one of themanners described below to limit contact of the operative element to theintended bodily structure.

As shown by way of example in FIG. 66, a guidewire 286 may be used todirect and/or anchor the distal leg 278 of the exemplary spline assembly272 in an anatomical anchor site (such as one of the pulmonary veinsshown in FIG. 66). The guidewire 286 passes through a lumen in the shaft254. The distal end of the guidewire 286 passes through a lumen 288formed in one of the spline assembly side legs 274 and 276, while theproximal end is secured to a handle 290. Alternatively, two guide wires(one passing through each of the side legs) may be used to anchor thespline assembly 272 in two anatomical anchor sites. Both wires wouldextend to the same handle.

The exemplary embodiments illustrated in FIGS. 62-66 may also beprovided without the tubular member 264. Such devices are especiallyuseful in surgical procedures associated with a thoracotomy or a mediansternotomy, where the spline assemblies can be easily collapsed andadvanced to the desired location, or advanced into the desired locationwithout being collapsed. Here, the spline assemblies can be malleable,if desired, as opposed to simply being bendable.

Turning to FIGS. 67a and 67 b, an endoscope 292 may be passed throughone lumen in a tubular member 264′ that has a pair of lumens.Alternatively, the shaft 254 and endoscope 292 can pass through a commonlumen.

The spline assemblies illustrated in FIGS. 62-66 are preferably madefrom resilient, inert wire, like nickel titanium (commercially availableas Nitinol material) or 17-7 stainless steel. However, resilientinjection molded inert plastic can also be used. The wire or moldedplastic is covered by suitable biocompatible thermoplastic orelastomeric material such as PEBAX® or Pellethane®. Preferably, thevarious portions of the spline assemblies comprises a thin, rectilinearstrips of resilient metal or plastic material. Still, othercross-sectional and longitudinal configurations can be used. Forexample, the spline legs can decrease in cross-sectional area in adistal direction, by varying, e.g., thickness or width or diameter (ifround), to provide variable stiffness along its length. Variablestiffness can also be imparted by composition changes in materials or bydifferent material processing techniques. Referring more specifically tothe embodiments illustrated in FIGS. 64a-66, the distal leg 278 may beconfigured such that the leg is flat at the distal end, but becomes moresemicircular in cross-section as the leg becomes more proximal in orderto taper the stiffness profile and prevent lateral movement of thespline assembly. The curvature of the spline legs may also be varied andthe lateral ends of the distal leg may be reinforced in order to providemore lateral stability.

As shown by way of example in FIGS. 70a-70 e, the spline assembly of theprobe shown in FIGS. 64a and 65 may be replaced by a curved splineassembly 300. Here, the spline assembly includes a flat, inert wire 302(preferably formed from Nitinol) that acts as a spring and an outerportion 304 (preferably formed from PEBAX® or Pellethane®). Viewed incross-section, the flat wire 302 has a long side and a short side. Theshort sides lie in planes that are parallel to the plane shown in FIG.70d. As such, the spline assembly 300 will deflect in the manner shownin FIGS. 70b and 70 c when “in plane” forces F are applied to the splineassembly. Conversely, the assembly will resist bending when “out ofplane” forces are applied in the manner shown in FIG. 70d. As such, itmay be used to form an arcuate lesion during, for example, a procedurewhere a lesion is formed around the pulmonary vein.

It should be noted here that the wire 302 does not have to berectangular in cross-section as shown. Other cross-sectional shapeswhere the length is greater than the width can also be used. The wire302 can also be made from a malleable material such as partially orfully annealed stainless steel instead of the spring-like materialdiscussed above. The malleable embodiments will enable the operator toform fit the ablation element support structure to irregular anatomicalstructures.

As shown in FIG. 70f, exemplary spline assembly 300′ includes first andsecond steering wires 301 a and 301 b that are secured to thespring-like flat wire 302 by, for example, welding, mechanical crimpingor adhesive bonding. The proximal ends of the steering wires 301 a and301 b are operably connected to a knob 303 on a handle 266′ by way of acam (not shown). The handle 266′ is substantially similar to the handle266 shown in FIG. 62, but for the knob 303, cam and provisions for thesteering wires 301 a and 301 b. Rotation of the knob 303 will cause thespline assembly to move side to side in, for example, the mannerillustrated in FIG. 70c. Thus, in addition to simply moving the handle,the physician will be able to move the operative element 252 within thepatient by rotating the knob 303. Such movement is useful when thephysician is attempting to precisely locate the operative element withinthe patient and/or control the contact force between the operativeelement and the tissue surface. This is especially true when the handleand or shaft 254 cannot be moved, due to anatomical or surgicalconstraints.

In the exemplary embodiment, the steering wires 301 a and 301 b are bothsecured at about the midpoint of the flat wire loop. Otherconfigurations are possible depending on the configuration of the loopthat is desired after the knob 303 is rotated. For example, one wirecould be secured closer to the top of the loop than the other. The shapeof the cam may also be varied. More detailed discussions of the use ofsteering wires, albeit in conventional catheter settings, can be foundin commonly assigned U.S. Pat. No. Nos. 5,195,968, 5,257,451, and5,582,609, which are incorporated herein by reference.

The shaft 254 is preferably relatively stiff. As used herein the phrase“relatively stiff” means that the shaft (or other structural element) iseither rigid, malleable, or somewhat flexible. A rigid shaft cannot bebent. A malleable shaft is a shaft that can be readily bent by thephysician to a desired shape, without springing back when released, sothat it will remain in that shape during the surgical procedure. Thus,the stiffness of a malleable shaft must be low enough to allow the shaftto be bent, but high enough to resist bending when the forces associatedwith a surgical procedure are applied to the shaft. A somewhat flexibleshaft will bend and spring back when released. However, the forcerequired to bend the shaft must be substantial. Rigid and somewhatflexible shafts are preferably formed from stainless steel, whilemalleable shafts are formed from annealed stainless steel.

One method of quantifying the flexibility of a shaft, be it shafts inaccordance with the present inventions or the shafts of conventionalcatheters, is to look at the deflection of the shaft when one end isfixed in cantilever fashion and a force normal to the longitudinal axisof the shaft is applied somewhere between the ends. Such deflection (τ)is expressed as follows:

τ=WX ²(3L−X)/6EI

where:

W is the force applied normal to the longitudinal axis of the shaft,

L is the length of the shaft,

X is the distance between the fixed end of the shaft and the appliedforce,

E is the modulous of elasticity, and

I is the moment of inertia of the shaft.

When the force is applied to the free end of the shaft, deflection canbe expressed as follows:

τ=WL ³/3EI

Assuming that W and L are equal when comparing different shafts, therespective E and I values will determine how much the shafts will bend.In other words, the stiffness of a shaft is a function of the product ofE and I. This product is referred to herein as the “bending modulus.” Eis a property of the material that forms the shaft, while I is afunction of shaft geometry, wall thickness, etc. Therefore, a shaftformed from relatively soft material can have the same bending modulusas a shaft formed from relatively hard material, if the moment ofinertia of the softer shaft is sufficiently greater than that of theharder shaft.

For example, a relatively stiff 2 inch shaft (either malleable orsomewhat flexible) would have a bending modulus of at leastapproximately 1 lb.-in.². Preferably, a relatively stiff 2 inch shaftwill have a bending modulus of between approximately 3 lb.-in.² andapproximately 50 lb.-in.². By comparison, 2 inch piece of a conventionalcatheter shaft, which must be flexible enough to travel through veins,typically has bending modulus between approximately 0.1 lb.-in.² andapproximately 0.3 lb.-in.². It should be noted that the bending modulusranges discussed here are primarily associated with initial deflection.In other words, the bending modulus ranges are based on the amount offorce, applied at and normal to the free end of the longitudinal axis ofthe cantilevered shaft, that is needed to produce 1 inch of deflectionfrom an at rest (or no deflection) position.

As noted above, the deflection of a shaft depends on the composition ofthe shaft as well as its moment of inertia. The shaft could be made ofelastic material, plastic material, elasto-plastic material or acombination thereof. By designing the shaft 254 to be relatively stiff(and preferably malleable), the surgical tool is better adapted to theconstraints encountered during the surgical procedure. The forcerequired to bend a relatively stiff 2 inch long shaft should be in therange of approximately 1.5 lbs. to approximately 12 lbs. By comparison,the force required to bend a 2 inch piece of conventional catheter shaftshould be between approximately 0.2 lb. to 0.25 lb. Again, such forcevalues concern the amount of force, applied at and normal to the freeend of the longitudinal axis of the cantilevered shaft, that is neededto produce 1 inch of deflection from an at rest (or no deflection)position.

Ductile materials are preferable in many applications because suchmaterials can deform plastically before failure due to fracturing.Materials are classified as either ductile or brittle, based upon thepercentage of elongation when the fracture occurs. A material with morethan 5 percent elongation prior to fracture is generally consideredductile, while a material with less than 5 percent elongation prior tofracture is generally considered brittle. Material ductility can bebased on a comparison of the cross sectional area at fracture relativeto the original cross area. This characteristic is not dependent on theelastic properties of the material.

Alternatively, the shaft could be a mechanical component similar toshielded (metal spiral wind jacket) conduit or flexible Loc-Line®, whichis a linear set of interlocking ball and socket linkages that can have acenter lumen. These would be hinge-like segmented sections linearlyassembled to make the shaft.

The exemplary tubular member 264 illustrated in FIGS. 62-67b ispreferably in the form of a relatively thin cylindrical sheath (e.g.,with a wall thickness of about 0.005 inch) and has an outer diameterwhich is preferably less than 0.180 inch. The sheath material ispreferably also lubricious, to reduce friction during movement of thesheath relative to the shaft 254 and spline assemblies 256 and 272. Forexample, materials made from polytetrafluoroethylene (PTFE) can be usedfor the sheath. The distal end of the sheath should be relativelyflexible to prevent injury. If necessary, additional stiffness can beimparted to the remaining portion of the sheath by lining the sheathwith a braided material coated with PEBAX® material (comprisingpolyethel block amide related to nylon). Other compositions made fromPTFE braided with a stiff outer layer and other lubricious materials canbe used.

Alternatively, the tubular member 264 may be relatively stiff and formedfrom the materials described above with respect to the shaft 254.

As shown by way of example in FIG. 71a, a surgical probe 308 inaccordance with another embodiment of this invention includes arelatively stiff shaft 310, a handle 312 and a distal section 314. Theshaft 310 consists of a hypo-tube 316, which is either rigid orrelatively stiff, and an outer polymer tubing 318 over the hypo-tube. Arelatively stiff tube, either malleable or somewhat flexible, willpreferably have a bending modulus of between approximately 3 lb.-in.²and approximately 50 lb.-in.². The handle 312 is similar to the handle266 discussed above in that it includes a PC board 320 for connectingthe operative elements on the distal portion of the probe to a powersource. The handle 312 preferably consists of two molded handle halvesand is also provided with strain relief element 322. An operativeelement 254 (here, in the form of a plurality of electrode elements 294)is provided on the distal section 314. This embodiment is particularlyuseful because it can be easily inserted into the patient through anintroducing port such as a trocar.

The handle 312 shown in FIG. 71a is intended to be used in aconventional power supply configuration, wherein power transmission froman RF generator (or other energy source) to the electrodes 294 iscontrolled by a foot switch. As shown by way of example in FIG. 71d, andin accordance with one embodiment of a present invention, a handle 312′is provided with a manually operable on-off switch 313. On-off switch313 allows the physician to selectively enable and disable the supply ofRF ablation energy (and other types of power) to the electrode(s) on thedistal portion of the probe.

In addition to the global on-off switch 313, the exemplary handle 312″shown in FIG. 71e also includes a plurality of individual on-offswitches 315 for each of the electrodes. The individual on-off switches315 allow the physician to selectively control the supply of power toindividual electrodes. The exemplary handle 312″, which has sevenindividual on-off switches 315, is preferably used in a probe havingseven electrodes. If for example, the physician intends to ablate tissuewith only three of the electrodes, then the three chosen electrodes maybe enabled by way of the corresponding switches 315 prior to placing theglobal on-off switch 313 in the “on” position.

A plurality of indicator elements 317 are also provided on the exemplaryhandle 312″ shown in FIG. 71e. Preferably, there is one indicatorelement 317 for each of the on-off switches 315. In the illustratedembodiment, the indicator elements 317 are in the form of buttons thatare raised when a corresponding on-off switch 315 is depressed. Thisprovides the physician with a tactile as well as visual indication ofthe on-off status of the switches 315. The indicator elements 317 mayalso be in the form of indicator lights. Sound-based indications of theon-off status of the switches 315 may also be used. For example, aspeaker on the handle or the power supply device may be employed toperiodically indicate which of the switches 315 are in the “on”position.

In accordance with another aspect of the present inventions, a probe maybe configured such that the handle is re-usable and the remainingportions of the probe are disposable or separately re-usable. Turning toFIGS. 71f and 71 g, exemplary handle 312″ includes an edge-typeconnector having a first portion 319 on the handle and a second portion321 on the remaining portion of the probe. In the illustratedembodiment, the remaining portion is primarily the shaft 310 which, asdescribed above, supports a plurality of electrode elements (not shown).

The first and second connector portions 319 and 321 have elements thatwill mechanically couple the handle to the remaining portion of theprobe and release the two when desired. The first and second connectorportions will also connect signal wires from the electrodes (or otheroperative elements) and temperature sensors to the energy source. Alocking mechanism (not shown) may be used to maintain the integrity ofthe connection between the two connector portions. A cable 323 may beprovided to connect the handle to an energy source.

The handles shown in FIGS. 71e-71 g may be used with any of the probesdisclosed herein and the features of such handles may be incorporatedinto any of the other handles disclosed herein.

As shown by way of example in FIGS. 71h and 71 i, and in accordance withone embodiment of a present invention, a remote power control unit 325may be used in conjunction with a surgical probe 308 or a catheter (notshown). The remote power control unit 325 includes a main body 327 a anda plurality of on/off switches 327 b. Preferably, there is one on/offswitch 327 b for each electrode and, in the illustrated embodiment,there are seven electrodes and seven on/off switches. The remote powercontrol unit can also include a global power on/off switch (not shown).Alternatively, a foot pedal (not shown) may be provided to perform thesame function.

The size and shape of the remote power control unit 325 allow it to beeasily grasped in one hand by the physician or other member of theoperating room staff. Preferably, the remote power control unit 325 isabout 8 inches in length, about 1.5 inches in width and about 0.5 inchesin thickness. Of course, the size and shape can be adjusted to suitparticular needs.

The remote power control unit 325 may be used in conjunction withconventional electrophysiology power control units, such as that shownin U.S. Pat. No. 5,545,193, that are connected to a source of energy(such as ablation energy) and provide individual electrode control. Tofacilitate such use, the remote control device includes a connectionapparatus which, in the illustrated embodiment, consists of a cable 329a and a connector 329 b. The cable 329 a should be relatively long, i.e.between about 6 feet and about 15 feet in length and is preferably 10feet. The connection apparatus can also be in the form of a wirelesstransmitter/receiver arrangement or any other suitable device. Thesurgical probe 308 is also connected to the electrophysiology powercontrol unit. When a foot pedal is used, it too is connected to theelectrophysiology power control unit.

The exemplary remote power control unit 325 includes indicia 333 in theshape of the distal portion of a surgical probe, indicator lights 335,and numbers corresponding to the respective electrodes on the probe. Thecombination of indicia, lights and numbers allows the physician toreadily determine which electrodes are enabled and which electrodes aredisabled.

The surgical probe 308 (as well as the other probes disclosed herein)and the remote power control unit 325 are sterilizable. To that end,these devices are either entirely hermetically sealed or selectedportions, such as those enclosing electronic components, are sealed.Those components which are not sealed are penetrable by a gas sterilant,such as ethylene oxide (EtO). The surgical probes and remote powercontrol units should also be splash-proof.

In those instances where a malleable shaft 310 is desired, the hypo-tube316 may be the heat treated malleable hypo-tube 316 shown in FIGS. 71a,73 and 74. By selectively heat treating certain portions of thehypo-tube, one section of the hypo-tube (preferably the distal section)can be made more malleable than the other. This will alleviate anydiscontinuity between the distal section 314 and the shaft 310 when thedistal section is malleable.

A plurality of temperature sensing elements (such as thermocouples whichare not shown) may be located on, under, abutting the longitudinal endedges of, or in between, the electrode elements 294 in any of theexemplary devices disclosed herein. Additionally, a referencetemperature sensing element may be provided. For example, a referencetemperature sensing 324 may be located in the handle so that roomtemperature will be used as the reference as shown in FIG. 71a. Thereference temperature sensor may, alternatively, be provided on or nearthe distal tip of the device. Another alternative is to use anelectronic circuit to function as the reference temperature sensor. Areference temperature sensor can also be placed on the patient or in theoperating room and the physician can simply input the referencetemperature into the power control device. It should be noted that theaccuracy of the reference temperature sensor is less important inapplications where the patient is on bypass because the convectivecooling effects of blood flowing past the electrodes is substantiallyreduced. Also, the present surgical devices provide better tissuecontact than conventional catheter-based devices, which provides moreaccurate temperature monitoring.

The distal section 314 can be either somewhat flexible, in that it willconform to a surface against which it is pressed and then spring back toits original shape when removed from the surface or, as noted above,malleable. A bending modulus of between 3 lb.-in.² and 50 lb.-in.² ispreferred. As shown by way of example in FIG. 72a, a somewhat flexibledistal section 314 may include a spring member 330, which is preferablyeither a solid flat wire spring (as shown), a round wire, or a threeleaf flat wire Nitinol spring, that is connected to the distal end ofthe hypo-tube 316. Other spring members, formed from materials such as17-7 or carpenters steel, may also be used. A series of lead wires 332and 334 connect the electrode elements 294 and temperature sensorelements, respectively, to the PC board 320. The spring member 330 andleads wires 332 and 334 are enclosed in a flexible body 336, preferablyformed from PEBAX® material, polyurethane, or other suitable materials.The spring member 330 may also be pre-stressed so that the distal tip ispre-bent in the manner shown in FIG. 71a. Also, an insulating sleeve 331may be placed between the spring member 330 and the lead wires 332 and334.

In those instances where a malleable distal portion 314 is desired, thespring member 330 may be replaced by a mandrel 337 made of suitablymalleable material such as annealed stainless steel or beryllium copper,as illustrated for example in FIG. 72b. The mandrel will ideally befixed to the distal tip of the device (by, for example, soldering, spotwelding or adhesives) and run through the shaft into the handle where itwill also be fixed to insure good torque transmission and stability ofthe distal tip. Alternatively, the malleable mandrel may be fixeddirectly within the distal end of the shaft's hypo-tube 316 and securedby, for example, soldering, spot welding or adhesives.

Alternatively, and as shown by way of example in FIG. 72c, a slot 339may be formed in the hypotube 316′. The malleable mandrel 337 isinserted into the slot 339 and then held in place by spot welds 341(shown), solder or adhesive. The slot 339 includes an opening 341 at oneend thereof through which the mandrel 337 extends. The slot 339 couldalso include another opening at the other end. The slot 339 is locatedin spaced relation to the proximal end of the hypotube 316′ to createadditional support for the mandrel 337 when it is bent and formed intovarious shapes. By shortening the length of the mandrel 337, the torqueof the shaped distal assembly is increased relative to the embodimentdescribed above wherein the mandrel is anchored within the handle.

The distal portion 314 may also be formed by a hypo-tube that is simplya continuation of the shaft hypo-tube 316. However, the distal endhypo-tube can be a separate element connected to the shaft hypo-tube316, if it is desired that the distal end hypo-tube have differentstiffness (or bending) properties than the shaft hypo-tube.

The shaft 310 may be from 4 inches to 18 inches in length and ispreferably 6 to 8 inches. The distal portion 314 may be from 1 inch to10 inches in length and is preferably 2 to 3 inches. To facilitate theformation of long continuous lesions, the distal portion 314 preferablyincludes six spaced electrode elements 294 that are approximately 12 mmin length. The number and length of the electrode elements 294 can, ofcourse, be varied to suit particular applications.

In accordance with some embodiments of this invention, and as shown byway of example in FIGS. 71b and 71 c, the distal section 314 may beprovided with a distal (or tip) electrode. Referring first to FIG. 71b,the distal electrode 326 may be a solid electrode with a through holefor one or more temperature sensors. Another exemplary electrode is theshell electrode 328 shown in FIG. 71c, which could also have one or moretemperature sensors inside. The distal electrodes have a variety ofapplications. For example, a distal electrode may be dragged along ananatomical surface to create a long lesion. The distal electrode mayalso be used to touch up lesions (straight or curvilinear) created byelectrode elements 294 if, for example, the distal section 314 does notexactly conform to the anatomical surface, and to continue lesionsformed by the electrode elements. The distal electrode may also be usedto create lesions in anatomical ridges that are shaped such that theintegrity of the surgical device would be compromised if the distalsection 314 were bent to conform to the ridge.

As shown by way of example in FIG. 74, an exemplary surgical probe 340is provided with a pull wire 342 that allows the physician to adjust thecurvature of the distal portion 314 from no curve, to a slight curve, anextreme curve, or even a loop, as desired. The pull wire distal portion344 is connected to the distal tip of distal section 314. The distalportion of the pull wire enters the shaft proximal to the ablationelectrodes, and the proximal portion 346 exits through an apertureformed in the handle 312. But for the pull wire 342, the probe 340 issubstantially the same as the spring tip probe version shown in FIGS.71a and 72 a. Alternatively, the proximal portion of the pull wire 342may be associated with a handle/knob arrangement such as that shown inFIG. 70f.

In accordance with another embodiment of this invention, and asillustrated for example in FIGS. 75 and 76, a surgical probe 348 isprovided with a distal loop structure 350 that includes an operativeelement 252 in the form of a plurality of electrodes 294. The distalloop structure 350, which extends through an opening 352 in a sheath354, is connected to a shaft 356. The shaft is, in turn, connected tothe handle 312. The proximal portion of the sheath 354 includes a handle358 that allows the sheath to be moved distally and proximally. Thestiffness of the loop structure 350 is less than that of the sheath 354.As such, when the sheath 354 is pulled in the proximal direction, theloop structure 350 will bulge out of the sheath opening 352 in themanner shown in FIG. 75. When the sheath 354 is returned to its distalmost position, the loop structure 350 will slide back into the sheathsuch that the sheath and the loop structure are coaxial.

The exemplary loop structure 350 is similar to the distal portion 314 ofthe probe shown in FIGS. 71a and 72 a in that it includes a springmember (not shown), such as a leaf spring or a flat wire spring(preferably formed from Nitinol), which is covered by a flexiblematerial such as a PEBAX® tube 359. In addition to allowing the distalportion 350 to bulge outwardly, the spring member can be flat so that italso provides resilience which helps the distal portion conform to theanatomical surface of interest and prevents “out of plane bending.”

In the exemplary embodiment illustrated in FIGS. 75 and 76, a pivotassembly 360 is provided on the distal end of the sheath 354. The pivotassembly 360 includes a base member 362 and a pivot member 364 which issecured to the base member by a pivot pin 366. Referring morespecifically to FIG. 76, the pivot member 364 pivots within a slot 368that is formed in the base member 362. The size and shape of the slot368, and the location of the pivot member 364 therein, may be adjustedto adjust the shape of the loop. For example, the location of the pivotmember 364 and the shape and size of the slot 368 may be varied suchthat the pivot member can only rotate 30, 60, 90 or 180°. However, up to270° of rotation is possible. The pivot member 364 includes a connector372 (such as the illustrated threaded or barbed connector) for securingthe distal end of the loop structure 350 to the pivot member.

The rigidity, malleability, or flexibility of the probe 348 may beprovided in a number of ways. For example, the sheath 354 may be formedfrom a rigid stainless steel hypo-tube, a relatively stiff somewhatflexible stainless steel hypotube, or a relatively stiff malleableannealed stainless steel hypo-tube. Additionally, or alternatively, theshaft 356 may be a rigid (or somewhat flexible) stainless steelhypo-tube or a malleable annealed stainless steel hypo-tube. In eithercase, the distal end 374 of the shaft 356 will abut the flexible portionof the loop structure 350. Other materials can, of course, be used inplace of stainless steel. A rigid high durometer plastic tube, forexample, may be substituted for the stainless steel hypo-tube in thesheath or shaft.

Once the sheath 354 and shaft 356 are positioned relative to one anothersuch that the desired loop is produced, the sheath may be secured to theshaft by a touhy borst connector 376 that is secured to the distal endof the sheath 354 between the handle 358 and the handle 312.

An ablation probe 378 in accordance with another aspect of thisinvention is illustrated, for example, in FIG. 77. The probe includes ashaft 380 (similar to shafts 254, 310 or 356 described above) on whichone or more ablation electrodes 294 are mounted. As described in greaterdetail in Section III below, masking 296 may be used to control thefocus of the ablation energy and/or prevent convective cooling when theprobe is in the blood pool. A handle 266 is also provided. The shaft 380is preferably between approximately 4 and 16 inches in length, betweenapproximately 3 and 8 mm in diameter. Additionally, the shaft may eitherbe rigid or relatively stiff and, if relatively stiff, can be eithermalleable or somewhat flexible. The ablation probe 378 may be used for avariety of procedures. For example, the shaft may be inserted into theheart to perform ablation procedures.

Turning to FIGS. 95 and 96, a pressure application probe 650 may be usedto apply pressure to the distal section of a probe, such as the probe308 shown in FIG. 71a, or any other operative element supporting device.The application of pressure with the probe 650 can improve the level ofcontact between tissue and, for example, the distal section 314 of theprobe 308. The pressure application probe 650 includes an elongate mainbody portion 652 and at least one engagement device 654. The exemplarypressure application probe shown in FIGS. 95 and 96 also includes asecond engagement device 658. As discussed in detail below, the secondengagement device 658 has a slightly different shape than the engagementdevice 654.

The main body portion 652 is preferably either rigid, malleable orsomewhat flexible and about 4 inches to about 18 inches in length,although the length may be adjusted to suit particular applications.When a malleable main body portion is desired, the main body portion 652may be formed in the manner described above with respect to the shaft254, and preferably consists of a soft metal rod or tube, or a settableplastic rod or tube. For example, the shaft 254 may be formed from anickel titanium rod or tube, which is ductile at room temperature andwhich will straighten out at elevated temperatures such as those usedduring autoclave sterilization. Regardless of stiffness, the outersurface of the main body portion 652 should be covered with insulatingmaterial such as PEBA® or urethane. The engagement device 654 ispreferably formed from insulating material such as polycarbonate,urethane, glass filled thermoplastic or ABS.

The engagement device may have any of a variety of configurations. Inthe exemplary embodiment illustrated in FIGS. 95 and 96, the engagementdevices 654 and 658 are generally c-shaped, with engagement device 658having a more open shape. In use, the c-shape helps maintain theengagement devices at the desired location on the distal portion of thesurgical probe 308 so that pressure can be applied to the desiredlocation. The open shape of the engagement device 658 allows theengagement device to be readily repositioned along the distal portion ofthe surgical probe without disturbing the position of the surgical proberelative to the tissue.

The c-shaped engagement device 654 can be coupled to the distal section314 of the probe 308 as shown in FIG. 95, or any other probe, by eitherinserting the distal tip of the probe through the opening 656 or bysnap-fitting the engagement device 654 over the distal section. Whensnap-fitting is desired, the engagement device should be somewhatflexible. This arrangement allows the pressure application probe 650 tobe rotated relative to the probe 308 when the two are engaged. As aresult, the pressure application probe 650 can be reoriented withoutmoving the probe 308. The pressure application probe 650 may also beused to move the probe 308 within the patient when the two are engaged.

As shown by way of example in FIG. 97, an exemplary pressure applicationprobe 660 is provided with an engagement device 662 having a relativelynarrow profile. The narrow profile allows the probe 660 to engage thedistal section of an operative element supporting device, such as thedistal section 314 of probe 308, even when the two devices are orientedat severe angles relative to one another. Of course, the engagementdevice is not limited to the shapes shown in FIGS. 95-97. Any shape thatis capable of engaging the distal portion of a probe may be used.

Although not limited to such a use, the pressure application probesshown in FIGS. 95-97 are especially useful in thoroscopic procedures.Here, the pressure application probe may be inserted into a patientthrough one port, while the electrode supporting probe is insertedthrough another port and connected to the pressure application probe.

Another device which may be used in conjunction with probes such as theprobe 308 shown in FIG. 71a is illustrated, for example, in FIG. 98. Theexemplary coupling device 664 includes a base member 666, a generallyc-shaped engagement device 668 (similar to that described above) and, inthe illustrated embodiment, a connecting member 670. The base member 666and engagement device 668 can also be directly connected to one another.

The coupling device 664 has a wide range of uses. For example, thecoupling device may part of a pressure application probe 672, as shownin FIG. 99. Another exemplary use of the coupling device 664 is shown inFIG. 100. Here, the coupling device 664 is placed on a probe such asprobe 308 and used to create a distal loop. The coupling device can belocated at different points along the length of the probe and arrangedat different rotational orientations relative to the probe (note arrows674 a and 674 b) in order to control the shape of the loop. To that end,the base member 666 and a portion of the distal section 314 can includerespective sets of teeth that allow the rotational orientation of thecoupling device 664 to be fixed relative to the probe 308. Note teeth676 in FIG. 101.

In order to increase the number of coupling device applications, theconnecting member 670 may be configured in a variety of ways. Forexample, the connecting member 670 can be rigid, flexible, somewhatflexible, or malleable. The connecting member 670 can also be in theform of a swivel or pivot. The base member 666 and engagement device 668can also be fixed at various angles relative to one another (note, forexample, FIG. 99).

III. The Operative Elements

A. Exemplary Operative Elements

In the exemplary embodiments illustrated in FIGS. 62-77, the operativeelement 252 is made up of a plurality of electrode elements 294.Electrode elements 294 can serve a variety of different purposes, as canelectrode elements 28 and 30 (FIGS. 1-61). The operative elements 252may also be lumens for chemical ablation, laser arrays, ultrasonictransducers, microwave electrodes, and D.C. hot wires, and such devicesmay be substituted for the electrode elements 28 and 30.

In the illustrated embodiments, the principal use of the electrodeelements is to transmit electrical energy and, more particularly, RFenergy, to ablate heart tissue. However, the electrode elements can alsobe used to sense electrical events in heart tissue. Alternatively, or inaddition, the electrode elements can serve to transmit electrical pulsesto measure the impedance of heart tissue, to pace heart tissue, or toassess tissue contact using conventional pacing and sensing techniques.Once the physician establishes contact with tissue in the desired heartregion, the physician applies ablating energy to the electrode elements.

In the exemplary embodiments shown in FIGS. 1-61, the electrode elements28 are electrically coupled to individual wires 58 (see FIG. 11a) toconduct ablating energy to them. The wires 58 extend along theassociated spline leg 22 (as FIG. 11a shows), through a suitable accessopening provided in the base 24 (for example, the anchor lumen 226 shownin FIG. 6b) into and through the catheter body lumen 36 (as generallyshown in FIG. 1 and FIGS. 30a/b), and into the handle 18, where they areelectrically coupled to external connectors 38 (see FIG. 1). Theconnectors 38 plug into a source of RF ablation energy (not shown).

Turning to the exemplary embodiments illustrated in FIGS. 62-77, theelectrode elements 294 are electrically coupled to individual wires (seereference numeral 295FIGS. 69b and 70 e and reference numeral 332 inFIGS. 72a, 72 b and 73) to conduct ablating energy to them. The wiresare passed in conventional fashion through a lumen extending through oneof the spline legs and the shaft 254 into a PC board in the handle 266,where they are electrically coupled to a connector 296 which is receivedin a port 298 (see FIG. 62). The connector 296 plugs into a source of RFablation energy. A plurality of temperature sensing elements (notshown), such as theremocouples or thermistors, may also be provided onthe spline assemblies shown herein. Such temperature sensing elementsmay be located on, under, abutting the longitudinal end edges of, or inbetween, the electrode elements 294. For temperature control purposes,signals from the temperature sensor elements are transmitted to thesource of ablation energy by way of wires (see reference numeral 297 inFIGS. 69b and 70 e and reference numeral 334 in FIGS. 72a, 72 b and 73)which are also connected to the PC board. Suitable temperature sensorelements and controllers which control power to an electrode based on asensed temperature are disclosed in U.S. Pat. No. Nos. 5,456,682 and5,582,609, which are incorporated herein by reference. The respectivenumbers of wires will, of course, depend on the numbers of sensors andelectrodes used in a particular application. A suitable temperaturecontrol system is described below with reference to FIGS. 89-92.

The electrode elements can be assembled in various ways. They can, forexample, comprise multiple, generally rigid electrode elements arrangedin a spaced apart, segmented relationship. The segmented electrodes caneach comprise solid rings of conductive material, like platinum, whichmakes an interference fit about the annular spline member.Alternatively, the electrode segments can comprise a conductivematerial, like platinum-iridium or gold, coated upon the device usingconventional coating techniques or an ion beam assisted deposition(IBAD) process. For better adherence, an undercoating of nickel ortitanium can be applied. The electrodes can also be in the form ofhelical ribbons.

Alternatively, the electrode elements can comprise spaced apart lengthsof closely wound, spiral coils wrapped about the device to form an arrayof generally flexible electrode elements. The coils are made ofelectrically conducting material, like copper alloy, platinum, orstainless steel, or compositions such as drawn-filled tubing (e.g. acopper core with a platinum jacket). The electrically conductingmaterial of the coils can be further coated with platinum-iridium orgold to improve its conduction properties and biocompatibility.

Electrode elements can be formed with a conductive ink compound that ispad printed onto a non-conductive tubular body. A preferred conductiveink compound is a silver-based flexible adhesive conductive ink(polyurethane binder), however other metal-based adhesive conductiveinks such as platinum-based, gold-based, copper-based, etc., may also beused to form electrodes. Such inks are more flexible than epoxy-basedinks.

As illustrated for example in FIG. 68, the electrode elements can alsoinclude a porous material coating 299, which transmits ablation energythrough an electrified ionic medium. For example, as disclosed in U.S.application Ser. No. 08/879,343, filed Jun. 20, 1997, entitled “SurfaceCoatings For Catheters, Direct Contacting Diagnostic and TherapeuticDevices,” which is incorporated herein by reference, electrode elementsand temperature sensor elements may be coated with regeneratedcellulose, hydrogel or plastic having electrically conductivecomponents. With respect to regenerated cellulose, the coating acts as amechanical barrier between the surgical device components, such aselectrodes, preventing ingress of blood cells, infectious agents, suchas viruses and bacteria, and large biological molecules such asproteins, while providing electrical contact to the human body. Theregenerated cellulose coating also acts as a biocompatible barrierbetween the device components and the human body, whereby the componentscan now be made from materials that are somewhat toxic (such as silveror copper).

For applications in which the ablation electrode is in contact withflowing blood as well as tissue, such as when the patient is not onbypass, coating electrodes with regenerated cellulose decreases theeffect of convective cooling on the electrode because regeneratedcellulose is a poor thermal conductor as compared to metal. Thus, theeffect of convective cooling by blood flowing past the regeneratedcellulose coated electrodes is diminished. This provides better controlfor a lesion-generating process because the hottest tissue temperatureis closer to the ablation electrode.

Furthermore, the regenerated cellulose coating decreases the edgeeffects attributed to delivering RF energy to an electrode having asharp transition between the conductive electrode and insulatingmaterial. The current density along the electrode and power densitywithin tissue are more uniform, which reduces the incidence and severityof char and/or coagulum formation. The more uniform current densityalong the axis of the device also results in a more uniform temperaturedistribution at the electrode, which decreases the requirement forprecise placements of the temperature sensors at the ablationelectrodes. Additionally, by coating a device with regenerated celluloseto create the outer surface, less labor-intensive methods of formingelectrodes and bonding wires to electrode surfaces can be used.

During the coating process, a device such as the one of theabove-described distal spline assemblies is coated with a viscosesolution. The viscose solution is preferably cellulose xanthate, whichis a form of solubilized cellulose derivative that is dissolved in asodium hydroxide solution. The viscose solution is dip-coated onto thedistal end assembly, which includes the electrodes, signal wires,temperature sensors, etc. The coated device is then regenerated bycontacting it with an acid, such as sulfuric acid, which converts thexanthate back into the cellulose structure. The term regeneratedcellulose refers to cellulose which has been converted from asolubilized cellulose derivative back into a pure cellulose structure.This regeneration process creates large enough micro size pores in thecoating allowing ionic transport yet small enough to prevent ingress ofblood cells, infectious agents, such as viruses and bacteria, and largebiological molecules such as proteins.

Once the cellulose is regenerated, it is rinsed with water to removeacid residuals and sulfur compounds. An oxidizing agent (bleach, etc.)may be added to the rinse water to accelerate the removal of sulfurcompounds. After the cellulose is regenerated, it is fully cured in anenvironmental chamber at a low humidity. Thereafter, it is preferable tomake the regenerated cellulose flexible when dry, and to do so moistureis reintroduced into the cellulose coating material by setting theenvironmental chamber to a higher humidity. Alternatively, a smallquantity of a material such as glycerol may be applied to the coating,and the hydroscopic nature of the glycerol will hydrate the cellulosecoating to create sufficient flexibility. An overall thickness range foroperable regenerated cellulose coatings is from 0.001 inches to 0.015inches, with a preferable thickness range being from 0.001 inches to0.003 inches; a preferred thickness being approximately 0.002 inches.

Materials other than regenerated cellulose that are mechanically robustand that have suitable characteristics could be used for the coatingmaterial. Hydrophilic materials that have effective pore sizes from 500to 500,000 Daltons with a porosity of 1-10% and which are biocompatiblecould be effective. Some types of hydrogels, such as those used fordisposable contact lenses are good candidate materials. Plasticmaterials that have additives to make them semiconductive could also beused. The loaded plastic would need to have a resistivity in the rangeof about 200-2,000 ohm-cm, and would need to be applicable in very thinfilms to the device.

The thickness of the cellulose coating is controlled by the viscosity ofthe coating solution and the dipping rate, and a different viscosity ofthe coating solution can be achieved by diluting it with the sodiumhydroxide solution. A variable wall thickness can be achieved by varyingthe extraction rate during the dipping process. The slower theextraction rate, the thinner the wall thickness, and the faster theextraction rate, the thicker the wall thickness. An increased coatingwall thickness can also be obtained by multiple layers of coating. Toensure proper lamination between such layers, each layer is coagulatedwith a salt solution (sodium sulfate, etc.) before applying anotherlayer. In addition, spraying and co-extruding the viscose solution overthe electrodes and the distal section can also be used to achieve avariable wall thickness cellulose coating.

In another method for covering a distal electrode assembly, a tubularcasing of regenerated cellulose material is created on a mandrel. Theregenerated cellulose casing is then shrunk onto the distal assembly.

The regenerated cellulose coating may also be applied over a “wet”electrode element. The moisture from the wet electrode element preventsthe electrode elements from sticking to tissue during an ablationprocedure. A wet electrode element is formed by a material that has highabsorption capacity for liquids, such as an open cell sponge, hydrogelor cloth. Alternatively, the regenerated cellulose coating may simply bewet prior to the procedure, such as an ablation procedure.

The electrode elements may be operated in a uni-polar mode, in which theablation energy emitted by the electrode elements is returned through anindifferent patch electrode (not shown) externally attached to the skinof the patient. Alternatively, the elements may be operated in abi-polar mode, in which ablation energy emitted by one or more electrodeelements is returned through other electrode elements. The amount ofpower required to ablate tissue ranges from 5 to 150 w.

The electrode elements are preferably about 4 mm to about 20 mm inlength. For example, the size and spacing of the electrode elements 28shown in FIGS. 10 and 11a/b are well suited for creating continuous,long and curvilinear lesion patterns in tissue when ablation energy isapplied simultaneously to adjacent emitting electrode elements.Continuous lesion patterns uniformly result when adjacent electrodeelements are spaced no farther than about 2.5 times the electrodesegment diameter apart. Further details of the formation of continuous,long and thin lesion patterns are found in co-pending U.S. applicationSer. No. 08/763,169, filed Dec. 10, 1996, which is a File WrapperContinuation of U.S. application Ser. No. 08/287,192, filed Aug. 8,1994, entitled “Systems and Methods for Forming Elongated LesionPatterns in Body Tissue Using Straight or Curvilinear ElectrodeElements,” which is incorporated herein by reference. Similar sizing andspacing may be used in conjunction with the other embodimentsillustrated herein.

Using rigid electrode segments, the length of the each electrode segmentcan vary from about 2 mm to about 10 mm. Using multiple rigid electrodesegments longer than about 10 mm each adversely effects the overallflexibility of the element. Generally speaking, adjacent rigid electrodesegments having lengths of less than about 2 mm do not consistently formthe desired continuous lesion patterns.

When flexible electrode segments are used, electrode segments longerthat about 10 mm in length can be used. Flexible electrode segments canbe as long as 50 mm. If desired, the flexible electrode structure canextend uninterrupted along the entire length of a support spline.

The diameter of the electrode segments 30 or 34 (FIGS. 1-61) andunderlying spline leg 22 (including the flexible sleeve 32) can varyfrom about 2 French to about 10 French.

B. Operative Element Considerations in a Non-Convective CoolingEnvironment

In the exemplary embodiments shown in, for example, FIGS. 15-20, 62-67a, 68, 70 a-f, 71, 74 and 75, the electrode elements are not masked.Such embodiments are particularly useful when little to no fluid flowwill be present, such as when the heart is on bypass and there is noblood flow within the heart. Here, air acts as an insulator and producesonly modest convective cooling effects, as compared to a flowing bloodpool that has a higher convection coefficient than virtually static air.Energy transmission is, therefore, essentially limited to the RF energythat is transmitted from the portion of the electrode surface that is incontact with the tissue to either a ground electrode, or anotherelectrode within the group of electrode elements. The overall impedanceof the system will increase (as compared to a situation where blood ispresent) due to the smaller effective surface area between the electrodeand tissue.

Both of these conditions, focused RF energy and low heat dissipationinto the air, will impact the ablation because they result in a highcurrent density with high local desposition of heat without the heatsinking that convective cooling provides. When creating long lesionswith a conventional catheter, char can be created as the tip is draggedbecause of the high current density and the difficulty in monitoringtissue temperature and controlling power that is inherent in thedragging process. The present invention, however, can take advantage ofthe high current density because the electrodes are not being dragged.For example, a number of electrodes can be used to ablate simultaneouslybecause the effective (tissue contacting) surface area between all ofthe ablating electrodes is smaller and the convective cooling effectsare reduced, as compared to situations where blood is present. Thisreduces the power requirements of the system. In addition, by usingelectrodes with lower thermal mass (as compared to a conventional solidtip electrode), less heat will be retained by the electrode and bettertemperature sensing can be made at the tissue surface. This will speedup the creation of the lesions and enable better lesion creationcontrol.

It is also noteworthy that the masking described in the followingsection can be useful during bypass because tissue can partially wraparound the electrodes when the distal end of the device is pressedagainst the tissue. Such masking can also be used to control lesionthickness.

C. Operative Element Considerations in a Convective Cooling Environment

In instances where the patient will not be on bypass and blood will beflowing past the electrodes, or in other situations when fluid flow ispresent, the portion of the electrode elements (or other operativeelements) not intended to contact tissue may be masked through a varietyof techniques with a material that is preferably electrically andthermally insulating. For example, a layer of UV adhesive (or anotheradhesive) may be painted on preselected portions of the electrodeelements to insulate the portions of the elements not intended tocontact tissue. Alternatively, a slotted sheath may be positioned overthe portion of the electrode elements not intended to contact tissue.Deposition techniques may also be implemented to position a conductivesurface only on those portions of the spline assembly intended tocontact tissue. A coating may be formed by dipping the electrodeelements in polytetrafluoroethylene (PTFE) material.

For example, as FIGS. 10 and 11b show, the side of the ablation elements28 that, in use, is exposed to the blood pool may be covered with acoating 48 of an electrically and thermally insulating material. Thecoating 48 prevents the transmission of ablating energy directly intothe blood pool. Instead, the coating 48 directs the applied ablatingenergy directly toward and into the tissue.

As shown by way of example in FIG. 69a, a polymer layer 296 may bethermally fused over the electrodes 294 to mask desired portions of theelectrodes. An exemplary process for applying the polymer layer is asfollows. A segment of shaft tubing is cut long enough to cover thedesired electrodes, and is then split in half (or other desired angle)along the axis. One half is placed over the assembled distal section sothat it covers the side of the electrodes that are to be masked. A pieceof polymeric shrink tubing, preferably RNF-100 or irradiated LDPE, isthen carefully slid over the catheter distal end, so that the masktubing is not moved from its placement over the electrodes and so thatit stops approximately 2 cm beyond the end of the tubing half. Thedistal end is then heated in a controlled heat source at approximately400° F. so that the mask tubing fuses into the distal shaft tubing alongits length, and so that all of its edges are well fused into the shafttubing, but not fused so much that the covered electrodes begin to pokethrough. Finally, the polymeric shrink tubing is split on one end andthe assembly is heated at approximately 225° F. while the polymericshrink tubing is slowly peeled off of the fused catheter shaft.

Additionally, as illustrated in FIG. 69b, the shape of an electrode 294′may be such that the metallic material in the region not intended tocontact tissue is eliminated.

The masking techniques described in the preceding paragraphs improve theefficiency of, for example, an ablation procedure by decreasing thesurface area of the electrodes and, therefore, the energy required toheat tissue. The masking can be used to form a narrow electrode which issometimes desirable, even when the patient will be on bypass. Theconvective cooling effects of blood flowing by the electrode are alsoreduced. In addition, the transmission of RF energy to unintendedanatomic structures is prevented. This is especially important inepicardial applications when the ablation electrode elements may besandwiched between multiple anatomic structures including, for example,the aorta and pulmonary artery. The masking techniques also focus theapplication of ablating energy to helps to control the characteristicsof the lesion.

IV. Epicardial Applications of Probe-Type Apparatus

The inventions described above (primarily those discussed above withreference to FIGS. 71a-75) may be used in a variety of epicardialprocedures. One such procedure is a maze-like ablation procedure toprevent atrial fibrillation. A thoracostomy, which is a surgicalprocedure that is less invasive than a thoracotomy or median sternotomy,may be used to gain access to the atrium. Here, relatively smallincisions are created in the intercostal space. At each of theincisions, a trocar may be used to provide a port to access the thoraciccavity. These ports may be used for visualization with fiberopticcameras, ultrasound, or other visualization devices, as well as for thesurgical devices that ablate tissue. The surgical devices may be, forexample, inserted through the ports located on the left side of thepatient which provide direct access to the left atrium. The devices maythen be used to create long, thin, curvilinear lesions or annularlesions on the epicardial surface. If necessary, lung lobes may bedeflated during the procedure by inserting an endotracheal tube thatinflates the right lung only. The left lung will collapse when the chestis opened.

There is also a high prevalence of atrial fibrillation substratesproximate to the pulmonary veins. Lesions may be created on theepicardial surface around pulmonary veins or between pulmonary veins.There is, however, some difficulty associated with epicardial access dueto the presence of fatty deposits in the pulmonary vein region. Thedevices described above can create lesions on the epicardial surfaceproximate to the pulmonary veins because they can penetrate throughfatty deposits and exert enough force against the epicardial surface tocompress the remaining fat to such an extent that the ablationelectrodes contact the epicardium. It is, however, very difficult toachieve suitable contact between the tissue and the electrodes. Thus, itis preferable to perform endocardial ablation around or betweenpulmonary veins in the manner described below.

V. Endocardial Applications of Probe-Type Apparatus

The inventions described above may be used in a variety of endocardialprocedures. To create lesions on the endocardial surface, access to theinterior of the left atrium must also be obtained. To obtainthoracoscopic access to the left atrium via a thoracostomy, a cannulamay be inserted through the left atrial appendage or the left atrialfree wall. The preferred access point is the left atrial appendage,especially if the physician intends to isolate the left atrial appendageat the end of the procedure. More specifically, and as shown by way ofexample in FIGS. 93 and 94, a grabbing catheter 642 having movablegrasping prongs 644, which is described in U.S. application Ser. No.08/880,711, filed Jun. 23, 1995, entitled “Atrial Appendage StasisReduction Procedures and Devices” may be used to capture, pull andstretch the appendage AP. Next, a lasso catheter 646 having a lasso 648,which is also described in U.S. application Ser. No. 08/880,711, may beused to encircle the left atrial appendage near the base of theappendage. The grabbing catheter facilitates the positioning of thelasso at the base of the appendage by pulling the appendage through thelasso. A needle is then used to puncture the appendage wall and gainaccess to the left atrium. A guidewire is advanced through the needleinto the left atrium. The needle is then removed, leaving the guidewirein place. An introducer/dilator combination is then advanced over theguidewire into the left atrium. Next, the lasso is then tightened aroundthe introducer to prevent blood flow past the introducer into the distalregion of the atrial appendage. The dilator is then removed, leaving theintroducer as the access to the interior of the left atrium.

Instead of the lasso technique, a purse string technique may be employedwherein sutures are used to tighten the atrial appendage around theintroducer.

One of the exemplary devices described above, such as those describedwith reference to FIGS. 1-70f, may then be inserted into the atrium withits spline collapsed. Once inside, the sheath is retracted such that thespline returns to its predetermined configuration and the ablationprocedure is performed. The sheath is pushed over the spline when theablation procedure is complete and the device is removed from theatrium. Similarly, the devices described above with reference to FIGS.75-76 may be inserted with the loop in its retracted state, while thedevice shown in FIG. 74 may be inserted prior to pulling the wireattached to the distal tip. These devices may then be manipulated tocause the loops to form. The ablation procedure can then be performed.The devices described above with reference to FIGS. 71a-c, 73 and 77need only be inserted to perform the procedure. The same is also truefor malleable versions of the exemplary devices shown in FIGS. 62-70e.

Upon completion, the introducer is removed and the lasso tightened toisolate the left atrial appendage. The lasso may be detached from theprobe and left in place to keep the appendage isolated. Where theaforementioned purse string technique is employed, the sutures may betightened isolate the appendage. Alternatively, the appendage may beisolated in the manner described below with reference to FIG. 87.

In addition to thoracoscopic procedures, another area of cardiactreatment which will benefit from the present invention is the repairand replacement of mitral valves (which typically involves athoracotomy, median sternotomy, or thoracostomy) because atrialfibrillation can be a complication of mitral disease which occurs priorto or subsequent to mitral valve surgery. More specifically, incisionalreentry can develop subsequent to surgical procedures (such as mitralvalve and thoracoscopic procedures) where an incision is made in theatrial wall that is subsequently closed by either sutures, mechanicalclosures, or other similar devices. Creating a lesion from the incisionto the mitral valve annulus (or other anatomic barrier) will reduce thepotential for reentrant propagation around the incision and, therefore,will terminate atrial fibrillation and/or prevent atrial fibrillationfrom developing. For example, if the left atrial appendage is used toaccess the interior of the left atrium for devices that create lesionson the endocardial surface, an additional lesion should be created fromthis access site to the mitral valve annulus so that incisional reentrywill not develop when the incision is closed. This additional procedureis also applicable for right atrial procedures using incisions to accessthe interior of the atrium.

There is also a high prevalence of atrial fibrillation substratesproximate to the pulmonary veins. The creation of long, curvilinearlesions between pulmonary veins, around single pulmonary veins, and/orfrom pulmonary veins to the mitral valve annulus will prevent atrialfibrillation. The exemplary device illustrated FIGS. 62 and 63, whichhas an annular electrode assembly, is especially well suited forpositioning ablation electrodes around the inside of a pulmonary vein.Alternatively, lesions may be created on the epicardial surface aroundpulmonary veins or between pulmonary veins. There is, however, somedifficulty associated with epicardial access due to the presence offatty deposits in the pulmonary vein region.

VI. Other Surgical Applications

A surgical method in accordance with a present invention may be used toreduce the level of bleeding during surgical procedures. The methodgenerally comprises the steps of coagulating (or ablating) tissue to apredetermined depth and then forming an incision in the coagulatedtissue. The coagulation can be accomplished by applying RF energy with,for example, the probe shown in FIG. 71a. Because the tissue iscoagulated, the incision will not result in bleeding.

One exemplary procedure employing the present method is the removal of adiseased liver lobe. This a relatively time consuming procedure and,using conventional surgical techniques, there is a significant risk ofserious bleeding. In accordance with one embodiment of the presentinvention, tissue in the lobe is coagulated to a depth of approximately3 mm to 7 mm using RF energy. The coagulated tissue is then cut andseparated with a scalpel, electro-surgical device, or other suitableinstrument. To avoid bleeding, the depth of the cut should not exceedthe depth of the coagulated tissue. The process of coagulating tissueand then forming an incision in the coagulated tissue can be repeateduntil the incision reaches the desired depth. Here, each coagulation andincision cycle will take approximately 90 seconds, 60 seconds to performthe coagulation and 30 seconds to perform the incision.

The present surgical technique is, of course, applicable to surgicalprocedures in addition to the removal of a liver lobe. Such proceduresmay, for example, involve the spleen, the kidneys, other areas of theliver, the heart, skeletal muscle, the lungs (such as a pulmonarylobotomy) and the brain. The present technique is also useful inoncological surgical procedures because cancerous tumors tend to behighly vascularized. One exemplary oncological procedure is thede-bulking of a cancerous tumor.

A surgical tool set in accordance with a present invention includes,among the other tools needed for a particular procedure, a device forcoagulating soft tissue and a cutting the tissue. Suitable devices forcoagulating soft tissue are illustrated for example, in FIGS. 62-88 and95-101. With respect to the probe shown in FIGS. 71f and 71 g, theportion of the probe which includes the second connector portion 321,the shaft 310 and a plurality of electrode elements can be included inthe tool set with or without the handle 312″. As noted above, scalpels,electro-surgical devices and other suitable instruments may be used tocut tissue. Preferably, the tool set is housed in a sterile package thathas a flat rigid bottom portion and a top transparent top cover thatprovides recesses for the tools, thereby providing a ready to usesurgical kit. The bottom portion may be formed from Tyvek® spun bondedplastic fibers, or other suitable materials, which allow the contents ofthe package to be sterilized after the tools are sealed within thepackage.

VII. Apparatus that Apply a Clamping Force

In accordance with another of the present inventions, and as shown byway of example in FIGS. 78-80, a clamp 382 includes a pair of clampmembers 384 and 386, which are pivotably secured to one another by a pin388, and an operative element 252 that may be of the type discussedabove in Section III. Here, the operative element consists of aplurality of ablation electrodes 294. The clamp 382 also includes a pairof locking members 390 and 392 and an electrical connector 394 that maybe used to, for example, connect the electrodes 294 to a source RFenergy. Referring more specifically to FIG. 80, the clamp 382 may also,if desired, be curved over its length. Of course, the overall shape ofthe clamp will depend upon the procedure for which it is intended.

Certain procedures require the application of a clamping force to thebodily structure of interest in addition to the operation performed bythe operative element. One such procedure is the isolation of an atrialappendage, which is discussed in greater detail below with reference toFIG. 87. As illustrated for example in FIG. 81, a suitable surgicaldevice 396 for use in such a procedure includes a handle 398 having apair of handle members 400 and 402 which are movable relative to oneanother. In the exemplary embodiment, the handle members are pivotablysecured to one another by a pin 404 and include respective openings 406and 408. The handle 398, which is actuated in a manner similar toscissors, is operably connected to a pair of support members 410 and 412by, for example, a suitable mechanical linkage located within a housing414. Actuation of the handle 398 causes the support members 410 and 412to move relative to one another to create a clamping force. Of course,other types of handles that can cause movement of the support membersmay also be used.

An operative element 252, is associated with one or both (as shown) ofthe support members 410 and 412. Preferably, the operative elementconsists of one or more electrode elements 294 suitable for ablation(such as those discussed in detail in Section III above and operable ineither the uni-polar or bi-polar mode) on each of the support members410 and 412. Of course, the operative element 252 may also consist inwhole or in part of other types of electrodes, such as a hot tip tocauterize appendage walls. The electrode elements 294 (or otheroperative element) may be connected to a control/power source surgicaldevice by way of a connector 416. Wires extend from the electrodeelements 294 through lumens in the support members 410 and 412 andhandle 398 to the connector 416.

Turning to FIG. 82, surgical device 418 is similar to that shown in FIG.81 except that handle 398 is not connected to the operative elementsupport members 410 and 412 by a mechanical linkage. Instead, the handlemember 420 and support member 422 form an integral unit as do the handlemember 424 and support member 426. The integral units are pivotablysecured to one another by a pin 428. Thus, while the embodiment shown inFIG. 81 is especially useful in situations where thoracostomy is used,the embodiment shown in FIG. 82 is especially useful for thoracotomy ormedian sternotomy access. In either case, the atrial appendage (or otherbodily structure) is captured (or clamped) such that it is perpendicularto the surgical device.

As shown by way of example in FIGS. 83 and 84, the operative elementsupport members 432 and 434 in exemplary surgical device 430 are securedto the distal ends of the handle members 436 and 438, respectively, suchthat the support members are perpendicular to the handle members.Although the handle members 436 and 438 are respectively secured to themiddle portion of the support members 432 and 434 (viewed longitudinallyas shown in FIG. 84), the support members may be offset in one directionor the other to suit particular needs (note FIG. 84a). Additionally, asillustrated for example in FIGS. 85a and 85 b, the support members (432′and 432″) may also be curved, or L-shaped with the angle θ between about90° and about 180°. The preferred embodiments shown in FIGS. 83-85b holdthe bodily structure such that it is parallel to the surgical device.

The exemplary embodiments shown in FIGS. 83-85b may be provided with aholding device that is used to grasp a bodily structure and pull thestructure in the proximal direction. As illustrated for example in FIG.86, the holding device 440 includes a cylindrical member 442 that isbiased in the proximal direction by a spring 444. A pair of clampingjaws 446 extend outwardly from the distal end of the cylindrical member442. The clamping jaws 446, which pivot relative to one another, areconnected to a rod 448 which passes through the cylindrical member 442and slides relative thereto. The rod 448 is biased in the proximaldirection by a spring 450 which, in turn, biases the clamping jaws 446in the proximal direction against the distal end of the cylindricalmember 442. As such, the clamping jaws 446 are biased to their closedposition and the jaws may be loosened by pushing the rod 448 in thedistal direction.

VIII. Applications of Apparatus that Apply a Clamping Force

The exemplary clamp 382 shown in FIGS. 78-80 can both isolate a bodilystructure and deliver the therapeutic and/or diagnostic effects of theoperative element 252. In an atrial appendage isolation procedure, forexample, the clamp 382 may be used to capture the atrial appendage andisolate it from the interior of the atrium. RF energy may then bedelivered via the electrodes 294 (in either the uni-polar mode or thebi-polar mode) to fuse the walls of the atrial appendage to one another.Thereafter, the clamp may either be removed, or disconnected from the RFenergy source and left in place.

Turning to FIG. 87, one exemplary use of the surgical device 396 shownin FIG. 81 is the isolation of an atrial appendage. Here, the device isinserted into an opening of the chest wall. The atrial appendage iscaptured between the support members 410 and 412 by actuating the handle398. RF energy is then transmitted, either from the electrodes 294 onone support member to the electrodes on the other (bi-polar mode) orfrom the electrodes to an indifferent reference electrode on, forexample, a patch (uni-polar mode) to thermally fuse the walls of theatrial appendage together and isolate the atrial appendage. The surgicaldevice shown in FIGS. 82-87 may be used in similar fashion.

As shown by way of example in FIG. 88, the operative element (such as,for example, electrodes 294) may be offset from one side or the other ofthe support members 452 and 454. This offset configuration, which may beused in conjunction with any of the exemplary devices shown in FIGS.81-86, is especially useful in an atrial appendage isolation procedure.Here, the electrodes 294 are offset from the side of the support members452 and 454 that is proximate to the interior of the left atrium. Bymaking the portions of the support members that do not support theelectrodes insulative, and by directing the RF energy towards the sideof the appendage (or other structure) isolated by the clamping force,coagulum or thrombus due to heating static blood will develop in theportion of the appendage that will be isolated from the blood pool whenthe side walls fuse to one another. Of course, when the patient is inbypass, such masking is unnecessary unless it is being used to createlesions of a certain shape.

IX. Power Control

A. General

FIG. 89 shows, in schematic form, a representative system 500 forapplying ablating energy by multiple emitters based, at least in part,upon local temperature conditions sensed by multiple sensing elements.

In FIG. 89, the multiple sensing elements comprise thermocouples 508,509, and 510 individually associated with the multiple emitters ofablating energy, which comprise electrode regions 501, 502, and 503. Thesystem 500 also includes a common reference thermocouple 511 carriedwithin the coupler element for exposure to the blood pool.Alternatively, other kinds of temperature sensing elements can be used,like, for example, thermistors, fluoroptic sensors, and resistivetemperature sensors, in which case the reference thermocouple 511 wouldtypically not be required.

The system 500 further includes an indifferent electrode 519 foroperation in a uni-polar mode.

The ablating energy emitters 501, 502, 503 can comprise the rigidelectrode segments previously described. Alternatively, the electroderegions 501, 502, 503 can comprise a continuous or segmented flexibleelectrode of wrapped wire or ribbon. It should be appreciated that thesystem 500 can be used in association with any ablating element thatemploys multiple, independently actuated ablating elements.

The system 500 includes a source 517 of ablating energy. In FIG. 89, thesource 517 generates radio frequency (RF) energy. The source 517 isconnected (through a conventional isolated output stage 516) to an arrayof power switches 514, one for each electrode region 501, 502, and 503.A connector 512 (carried by the probe handle) electrically couples eachelectrode region 501, 503, 503 to its own power switch 514 and to otherparts of the system 500.

The system 500 also includes a microcontroller 531 coupled via aninterface 530 to each power switch 514. The microcontroller 531 turns agiven power switch 514 on or off to deliver RF power from the source 517individually to the electrode regions 501, 502, and 503. The deliveredRF energy flows from the respective electrode region 501, 502, and 503,through tissue, to the indifferent electrode 519, which is connected tothe return path of the isolated output stage 516.

The power switch 514 and interface 530 configuration can vary accordingto the type of ablating energy being applied. FIG. 90 shows arepresentative implementation for applying RF ablating energy.

In this implementation, each power switch 514 includes an N-MOS powertransistor 535 and a P-MOS power transistor 536 coupled in between therespective electrode region 501, 502, and 503 and the isolated outputstage 516 of the power source 517.

A diode 533 conveys the positive phase of RF ablating energy to theelectrode region. A diode 534 conveys the negative phase of the RFablating energy to the electrode region. Resistors 537 and 538 bias theN-MOS and P-MOS power transistors 535 and 536 in conventional fashion.

The interface 530 for each power switch 514 includes two NPN transistors539 and 540. The emitter of the NPN transistor 539 is coupled to thegate of the N-MOS power transistor 535. The collector of the NPNtransistor 540 is coupled to the gate of the P-MOS power transistor 534.

The interface for each power switch 514 also includes a control bus 543coupled to the microcontroller 531. The control bus 543 connects eachpower switch 514 to digital ground (DGND) of the microcontroller 531.The control bus 543 also includes a (+) power line (+5V) connected tothe collector of the NPN transistor 539 and a (−) power line (−5V)connected to the emitter of the NPN interface transistor 540.

The control bus 543 for each power switch 514 further includes anE_(SEL) line. The base of the NPN transistor 539 is coupled to theE_(SEL) line of the control bus 543. The base of the NPN transistor 540is also coupled to the E_(SEL) line of the control bus 543 via the Zenerdiode 541 and a resistor 532. The E_(SEL) line connects to the cathodeof the Zener diode 541 through the resistor 532. The Zener diode 541 isselected so that the NPN transistor 540 turns on when E_(SEL) exceedsabout 3 volts (which, for the particular embodiment shown, is logic 1).

It should be appreciated that the interface 530 can be designed tohandle other logic level standards. In the particular embodiment, it isdesigned to handle conventional TTL (transistor transfer logic) levels.

The microcontroller 531 sets E_(SEL) of the control bus 543 either atlogic 1 or at logic 0. At logic 1, the gate of the N-MOS transistor 535is connected to (+) 5 volt line through the NPN transistors 539.Similarly, the gate of the P-MOS transistor 536 is connected to the (−)5 volt line through the NPN transistor 540. This conditions the powertransistors 535 and 536 to conduct RF voltage from the source 517 to theassociated electrode region. The power switch 514 is “on.”

When the microcontroller 531 sets E_(SEL) at logic 0, no current flowsthrough the NPN transistors 539 and 540. This conditions the powertransistors 535 and 536 to block the conduction of RF voltage to theassociated electrode region. The power switch 514 is “off.”

The system 500 (see FIG. 89) further includes two analog multiplexers(MUX) 524 and 525. The multiplexers 524 and 525 receive voltage inputfrom each thermocouple 508, 509, 510, and 511. The microcontroller 531controls both multiplexers 524 and 525 to select voltage inputs from themultiple temperature sensing thermocouples 508, 509, 510, and 511.

The voltage inputs from the thermocouples 508, 509, 510, and 511 aresent to front end signal conditioning electronics. The inputs areamplified by differential amplifier 526, which reads the voltagedifferences between the copper wires of the thermocouples 508/509/510and the reference thermocouple 511. The voltage differences areconditioned by element 527 and converted to digital codes by theanalog-to-digital converter 528. The look-up table 529 converts thedigital codes to temperature codes. The temperature codes are read bythe microcontroller 531.

The microcontroller 531 compares the temperature codes for eachthermocouple 508, 509, and 510 to preselected criteria to generatefeedback signals. The preselected criteria are inputted through a userinterface 532. These feedback signals control the interface powerswitches 514 via the interface 530, turning the electrodes 501, 502, and503 off and on.

The other multiplexer 525 connects the thermocouples 508, 509, 510, and511 selected by the microcontroller 531 to a temperature controller 515.The temperature controller 515 also includes front end signalconditioning electronics, as already described with reference toelements 526, 527, 528, and 529. These electronics convert the voltagedifferences between the copper wires of the thermocouples 508/509/510and the reference thermocouple 511 to temperature codes. The temperaturecodes are read by the controller and compared to preselected criteria togenerate feedback signals. These feedback signals control the amplitudeof the voltage (or current) generated by the source 517 for delivery tothe electrodes 501, 502, and 503.

Based upon the feedback signals of the microcontroller 531 and thetemperature controller 515, the system 500 distributes power to themultiple electrode regions 501, 502, and 503 to establish and maintain auniform distribution of temperatures along the ablating element. In thisway, the system 500 obtains safe and efficacious lesion formation usingmultiple emitters of ablating energy.

The system 500 can control the delivery of ablating energy in differentways. Representative modes will now be described.

B. Individual Amplitudes/Collective Duty Cycle

The electrode regions 501, 502, and 503 will be symbolically designatedE(J), where J represents a given electrode region (J=1 to N).

As before described, each electrode region E(J) has at least onetemperature sensing element 508, 509, and 510, which will be designatedS(J,K), where J represents the electrode region and K represents thenumber of temperature sensing elements on each electrode region (K=1 toM).

In this mode (see FIG. 91), the microcontroller 516 operates the powerswitch interface 530 to deliver RF power from the source 517 in multiplepulses of duty cycle 1/N.

With pulsed power delivery, the amount of power (P_(E(J))) conveyed toeach individual electrode is as follows:

P _(E(J))˜AMP_(E(J)) ²×DUTYCYCLE_(E(J))

where:

AMP_(E(J)) is the amplitude of the RF voltage conveyed to the electroderegion E(J), and

DUTYCYCLE_(E(J)) is the duty cycle of the pulse, expressed as follows:

DUTYCYCLE_(E(J))=TON_(E(J))/[TON_(E(J))+TOFF_(E(J))]

 where:

TON_(E(J)) is the time that the electrode region E(J) emits energyduring each pulse period,

TOFF_(E(J)) is the time that the electrode region E(J) does not emitenergy during each pulse period.

The expression TON_(E(J))+TOFF_(E(J)) represents the period of the pulsefor each electrode region E(J).

In this mode, the microcontroller 531 collectively establishes dutycycle (DUTYCYCLE_(E(J))) of 1/N for each electrode region (N being equalto the number of electrode regions).

The microcontroller 531 may sequence successive power pulses to adjacentelectrode regions so that the end of the duty cycle for the precedingpulse overlaps slightly with the beginning of the duty cycle for thenext pulse. This overlap in pulse duty cycles assures that the source517 applies power continuously, with no periods of interruption causedby open circuits during pulse switching between successive electroderegions.

In this mode, the temperature controller 515 makes individualadjustments to the amplitude of the RF voltage for each electrode region(AMP_(E(J))), thereby individually changing the power P_(E(J)) ofablating energy conveyed during the duty cycle to each electrode region,as controlled by the microcontroller 531.

In this mode, the microcontroller 531 cycles in successive dataacquisition sample periods. During each sample period, themicrocontroller 531 selects individual sensors S(J,K), and voltagedifferences are read by the controller 515 (through MUX 525) andconverted to temperature codes TEMP(J).

When there is more than one sensing element associated with a givenelectrode region, the controller 515 registers all sensed temperaturesfor the given electrode region and selects among these the highestsensed temperature, which constitutes TEMP(J).

In this mode, the controller 515 compares the temperature TEMP(J)locally sensed at each electrode E(J) during each data acquisitionperiod to a set point temperature TEMP_(SET) established by thephysician. Based upon this comparison, the controller 515 varies theamplitude AMP_(E(J)) of the RF voltage delivered to the electrode regionE(J), while the microcontroller 531 maintains the DUTYCYCLE_(E(J)) forthat electrode region and all other electrode regions, to establish andmaintain TEMP(J) at the set point temperature TEMP_(SET).

The set point temperature TEMP_(SET) can vary according to the judgmentof the physician and empirical data. A representative set pointtemperature for cardiac ablation is believed to lie in the range of 40°C. to 95° C., with 70° C. being a representative preferred value.

The manner in which the controller 515 governs AMP_(E(J)) canincorporate proportional control methods, proportional integralderivative (PID) control methods, or fuzzy logic control methods.

For example, using proportional control methods, if the temperaturesensed by the first sensing element TEMP(1)>TEMP_(SET), the controlsignal generated by the controller 515 individually reduces theamplitude AMP_(E(1)) of the RF voltage applied to the first electroderegion E(1), while the microcontroller 531 keeps the collective dutycycle DUTYCYCLE_(E(1)) for the first electrode region E(1) the same. Ifthe temperature sensed by the second sensing element TEMP(2)<TEMP_(SET),the control signal of the controller 515 increases the amplitudeAMP_(E(2)) of the pulse applied to the second electrode region E(2),while the microcontroller 531 keeps the collective duty cycleDUTYCYCLE_(E(2)) for the second electrode region E(2) the same asDUTYCYCLE_(E(1)), and so on. If the temperature sensed by a givensensing element is at the set point temperature TEMP_(SET), no change inRF voltage amplitude is made for the associated electrode region.

The controller 515 continuously processes voltage difference inputsduring successive data acquisition periods to individually adjustAMP_(E(J)) at each electrode region E(J), while the microcontroller 531keeps the collective duty cycle the same for all electrode regions E(J).In this way, the mode maintains a desired uniformity of temperaturealong the length of the ablating element.

Using a proportional integral differential (PID) control technique, thecontroller 515 takes into account not only instantaneous changes thatoccur in a given sample period, but also changes that have occurred inprevious sample periods and the rate at which these changes are varyingover time. Thus, using a PID control technique, the controller 515 willrespond differently to a given proportionally large instantaneousdifference between TEMP (J) and TEMP_(SET), depending upon whether thedifference is getting larger or smaller, compared to previousinstantaneous differences, and whether the rate at which the differenceis changing since previous sample periods is increasing or decreasing.

C. Deriving Predicted Hottest Temperature

Because of the heat exchange between the tissue and the electroderegion, the temperature sensing elements may not measure exactly themaximum temperature at the region. This is because the region of hottesttemperature occurs beneath the surface of the tissue at a depth of about0.5 to 2.0 mm from where the energy emitting electrode region (and theassociated sensing element) contacts the tissue. If the power is appliedto heat the tissue too quickly, the actual maximum tissue temperature inthis subsurface region may exceed 100° C. and lead to tissue desiccationand/or micro-explosion.

FIG. 92 shows an implementation of a neural network predictor 600, whichreceives as input the temperatures sensed by multiple sensing elementsS(J,K) at each electrode region, where J represents a given electroderegion (J=1 to N) and K represents the number of temperature sensingelements on each electrode region (K=1 to M). The predictor 600 outputsa predicted temperature of the hottest tissue region T_(MAXPRED)(t). Thecontroller 515 and microcontroller 531 derive the amplitude and dutycycle control signals based upon T_(MAXPRED)(t), in the same mannersalready described using TEMP(J).

The predictor 600 uses a two-layer neural network, although more hiddenlayers could be used. As shown in FIG. 91, the predictor 600 includesfirst and second hidden layers and four neurons, designated N_((L,X)),where L identifies the layer 1 or 2 and X identifies a neuron on thatlayer. The first layer (L=1) has three neurons (X=1 to 3), as followsN_((1,1)); N₍₁ ₂₎; and N_((1,3)). The second layer (L=2) comprising oneoutput neuron (X=1), designated N_((2,1)).

Temperature readings from the multiple sensing elements, only two ofwhich—TS1(n) and TS2(n)—are shown for purposes of illustration, areweighed and inputted to each neuron N_((1,1)); N_((1,2)); and N_((1,3))of the first layer. FIG. 31 represents the weights as W^(L) _((k,N)),where L=1; k is the input sensor order; and N is the input neuron number1, 2, or 3 of the first layer.

The output neuron N_((2,1)) of the second layer receives as inputs theweighted outputs of the neurons N_((1,1)); N_((1,2)); and N_((1,3)).FIG. 91 represents the output weights as W^(L) _((O,X)), where L=2; O isthe output neuron 1, 2, or 3 of the first layer; and X is the inputneuron number of the second layer. Based upon these weighted inputs, theoutput neuron N_((2,1)) predicts T_(MAXPRED)(t). Alternatively, asequence of past reading samples from each sensor could be used asinput. By doing this, a history term would contribute to the predictionof the hottest tissue temperature.

The predictor 600 must be trained on a known set of data containing thetemperature of the sensing elements TS1 and TS2 and the temperature ofthe hottest region, which have been previously acquired experimentally.For example, using a back-propagation model, the predictor 600 can betrained to predict the known hottest temperature of the data set withthe least mean square error. Once the training phase is completed thepredictor 600 can be used to predict T_(MAXPRED)(t).

Other types of data processing techniques can be used to deriveT_(MAXPRED)(t). See, e.g., co-pending U.S. application Ser. No.08/801,484, filed Feb. 18, 1997, which is a File Wrapper Continuation ofU.S. application Ser. No. 08/503,736, filed Jul. 18, 1995, which is aFile Wrapper Continuation of U.S. application Ser. No. 08/266,934, filedJun. 27, 1994, and entitled “Tissue Heating and Ablation Systems andMethods Using Predicted Temperature for Monitoring and Control.”

It should be noted that there are certain considerations which should betaken into account when ablation/coagulation procedures are performedwith little or no fluid present. Such procedures include, for example,procedures performed during cardiac bypass. These considerations stemfrom the fact that the convective cooling effects associated with airare far less than that associated with blood and other fluids. Inaddition, the intimate physical (and thermal) contact between theelectrodes and tissue will allow heat to be exchanged relatively freelytherebetween.

Because the electrodes which transmit RF energy have high conductivity,they will be subjected to much less ohmic heating. However, heat will bedrawn from the tissue to the electrode as RF power is applied to thetissue, which results in a time lag between hottest tissue temperatureand the temperature of the electrode as well as a temperature gradientwithin the tissue near the tissue surface. The electrode temperaturewill eventually approach the tissue temperature. At this point, therewill be a relatively small temperature gradient between the hottesttissue temperature and the electrode temperature, as well as relativelylittle heat transfer between the tissue and the electrode. Accordingly,the temperature control algorithm should take into account the time lagbetween the sub-surface tissue temperature and the temperature sensed atthe electrode. However, the difference between the plateau tissuetemperatures and the sensed temperatures can typically be disregarded.

In addition to the control considerations, the user interface shouldalso allow the physician to indicated whether convective cooling isgoing to be present, thereby allowing the physician to select the propertemperature control algorithm.

The illustrated and preferred embodiments used digital processingcontrolled by a computer to analyze information and generate feedbacksignals. It should be appreciated that other logic control circuitsusing micro-switches, AND/OR gates, invertors, analog circuits, and thelike are equivalent to the micro-processor controlled techniques shownin the preferred embodiment.

Although the present inventions have been described in terms of thepreferred embodiments above, numerous modifications and/or additions tothe above-described preferred embodiments would be readily apparent toone skilled in the art. It is intended that the scope of the presentinvention extends to all such modifications and/or additions.

We claim:
 1. A pressure application probe for use with a surgicaldevice, the surgical device including an elongate structure, defining adistal region, a distal region outer diameter not greater than about 5mm and a predetermined length sufficient to allow a physician tomanipulate the distal region when the elongate structure is insertedinto a body cavity through an incision, and at least one energytransmission device on the distal region, the pressure application probecomprising: an elongate main body portion defining a distal end, aproximal end and a length of at least four inches; and a unitarysubstantially c-shaped engagement device adapted to releasably engagethe surgical device elongate structure and including a pair of endsdefining an opening therebetween, a mid-portion secured to the main bodyportion and an interior region defining a size corresponding to thediameter of the distal region of the surgical device elongate structure.2. A pressure application probe as claimed in claim 1, wherein theengagement device is covered with electrically insulating material.
 3. Apressure application probe as claimed in claim 1, wherein the elongatemain body portion defines first and second longitudinal ends and thesubstantially c-shaped engagement device defines a first substantiallyc-shaped engagement device and is associated with the first longitudinalend of the main body portion, the pressure application probe furthercomprising: a second engagement device associated with the secondlongitudinal end of the main body portion and adapted to releasablyengage the surgical device elongate structure.
 4. A pressure applicationprobe as claimed in claim 1, wherein the pair of ends comprises a pairof free ends and the distal opening between the free ends of thec-shaped engagement device is wider than the distal region of thesurgical device elongate structure.
 5. A pressure application probe asclaimed in claim 1, wherein the main body portion defines a lengthcorresponding to the length of the surgical device elongate structure.6. A pressure application probe as claimed in claim 1, wherein the mainbody portion defines a length sufficient to allow a physician tomanipulate the distal end when the main body portion is inserted intothe thoracic cavity through an incision.
 7. A pressure application probeas claimed in claim 1, wherein the main body portion is malleable.
 8. Apressure application probe as claimed in claim 1, wherein the elongatemain body portion defines a length of at least 8 inches.
 9. A pressureapplication probe as claimed in claim 1, wherein the elongate main bodyportion defines a length of at least 12 inches.
 10. A pressureapplication probe as claimed in claim 1, wherein the ends of thec-shaped engagement device point distally.
 11. A surgical apparatus,comprising: an energy transmission probe including a handle and asupport member connected to the handle, the support member defining anexterior surface and having a having a proximal portion that is one ofrigid and malleable and a distal portion, and at least one energytransmission device on the distal portion of the support member; and apressure application probe including an elongate main body portion andan engagement device adapted to releasably engage the exterior surfaceof the support member and transmit distally directed force to thesupport member.
 12. A surgical apparatus as claimed in claim 11, whereinthe support member comprises relatively short shaft.
 13. A surgicalapparatus as claimed in claim 12, wherein the relatively short shaftdefines a distal end, the support member further comprising a bendablespline assembly associated with the distal end of the relatively shortshaft.
 14. A surgical apparatus as claimed in claim 11, wherein the atleast one energy transmission device comprises a plurality of energytransmission devices.
 15. A surgical apparatus as claimed in claim 11,wherein the engagement device comprises a generally c-shaped member. 16.A surgical apparatus as claimed in claim 11, wherein the engagementdevice is covered with electrically insulating material.
 17. A surgicalapparatus as claimed in claim 11, wherein the support member andengagement device are respectively constructed such that the pressureapplication probe can be moved relative to the energy transmission probewhen the pressure application probe and energy transmission probe areengaged.
 18. A surgical apparatus as claimed in claim 11, wherein theenergy transmission probe and pressure application probe are separatestructural elements that can be readily separated from one another. 19.A surgical apparatus as claimed in claim 11, wherein the pressureapplication probe includes a malleable elongate main body portion.
 20. Apressure application probe for use with a surgical device, the surgicaldevice including a shaft defining a distal end and a predeterminedlength sufficient to allow a physician to manipulate the distal end whenthe shaft is inserted into a body cavity through an incision, a supportmember associated with the distal end of the shaft and at least oneenergy transmission device on the support member, the pressureapplication probe comprising: an elongate main body portion defining alength substantially equal to the length of the surgical device shaft;and a unitary substantially c-shaped engagement device adapted toreleasably engage the support member and having a pair of ends definingan opening therebetween and a mid-portion secured to the main bodyportion.
 21. A method of forming a lesion in tissue, comprising thesteps of: providing an energy transmission probe including a supportmember and at least one energy transmission device on the supportmember; inserting the energy transmission probe directly into a bodilycavity through an incision in a patient; positioning the energytransmission probe within the patient such that the energy transmissiondevice is adjacent tissue; providing a pressure application probe;inserting the pressure application probe into the patient; engaging thesupport member with the pressure application probe; and transmittingenergy to the tissue through the at least one energy transmissiondevice.
 22. A method as claimed in claim 21, wherein the step ofpositioning the energy transmission probe within the patient comprisesinserting the support member through a first port and the step ofinserting the pressure application probe into the patient comprisesinserting the pressure application probe through a second port.
 23. Amethod as claimed in claim 21, further comprising the step of: applyingpressure to the support member with the pressure application probe. 24.A method as claimed in claim 21, further comprising the step of:reorienting the support member with the pressure application probe. 25.A method as claimed in claim 21, wherein the step of inserting theenergy transmission probe directly into a patient includes performingone of a thoracostomy, thoracotomy or median sternotomy prior toinserting the energy transmission probe into